SEC Info  
    Home      Search      My Interests      Help      Sign In      Please Sign In
 
We’re going down soon, to move to a new Data Center today.  We’ll be up ASAP.  Sorry.

Janus Henderson Group PLC – ‘10-K’ for 12/31/17 – ‘EX-101.DEF’

On:  Tuesday, 2/27/18, at 4:33pm ET   ·   For:  12/31/17   ·   Accession #:  1047469-18-1112   ·   File #:  1-38103

Previous ‘10-K’:  None   ·   Next:  ‘10-K’ on 2/26/19 for 12/31/18   ·   Latest:  ‘10-K’ on 2/27/24 for 12/31/23   ·   5 References:   

Find Words in Filings emoji
 
  in    Show  and   Hints

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 2/27/18  Janus Henderson Group PLC         10-K       12/31/17  120:26M                                    Toppan Merrill-FA

Annual Report   —   Form 10-K   —   Sect. 13 / 15(d) – SEA’34
Filing Table of Contents

Document/Exhibit                   Description                      Pages   Size 

 1: 10-K        Annual Report                                       HTML   2.38M 
 2: EX-4.1.5    Instrument Defining the Rights of Security Holders  HTML     59K 
 3: EX-10.19.7  Material Contract                                   HTML     53K 
 4: EX-10.19.8  Material Contract                                   HTML     33K 
 5: EX-10.24    Material Contract                                   HTML     35K 
 6: EX-10.25    Material Contract                                   HTML     95K 
 7: EX-10.32    Material Contract                                   HTML     92K 
 9: EX-21.1     Subsidiaries List                                   HTML     98K 
10: EX-23.1     Consent of Experts or Counsel                       HTML     28K 
 8: EX-12.1     Statement re: Computation of Ratios                 HTML     59K 
11: EX-31.1     Certification -- §302 - SOA'02                      HTML     35K 
12: EX-31.2     Certification -- §302 - SOA'02                      HTML     35K 
13: EX-31.3     Certification -- §302 - SOA'02                      HTML     35K 
14: EX-32.1     Certification -- §906 - SOA'02                      HTML     32K 
15: EX-32.2     Certification -- §906 - SOA'02                      HTML     32K 
16: EX-32.3     Certification -- §906 - SOA'02                      HTML     32K 
23: R1          Document and Entity Information                     HTML     58K 
24: R2          Consolidated Balance Sheets                         HTML    132K 
25: R3          Consolidated Balance Sheets (Parenthetical)         HTML     42K 
26: R4          Consolidated Statements of Comprehensive Income     HTML    126K 
27: R5          Consolidated Statements of Cash Flows               HTML    161K 
28: R6          Consolidated Statements of Changes in Equity        HTML    115K 
29: R7          Description of the Business                         HTML     34K 
30: R8          Summary of Significant Accounting Policies          HTML    134K 
31: R9          Recent Accounting Pronouncements                    HTML     45K 
32: R10         Acquisitions                                        HTML    133K 
33: R11         Consolidation                                       HTML     93K 
34: R12         Investment Securities                               HTML    548K 
35: R13         Goodwill and Intangible Assets                      HTML    121K 
36: R14         Equity Method Investments                           HTML     49K 
37: R15         Fair Value Measurements                             HTML    451K 
38: R16         Debt                                                HTML     90K 
39: R17         Income Taxes                                        HTML    289K 
40: R18         Other Financial Statement Captions                  HTML    115K 
41: R19         Noncontrolling Interests                            HTML    111K 
42: R20         Long-Term Incentive Compensation                    HTML    522K 
43: R21         Retirement Benefit Plans                            HTML    289K 
44: R22         Accumulated Other Comprehensive Loss                HTML    191K 
45: R23         Earnings and Dividends Per Share                    HTML    121K 
46: R24         Commitments and Contingencies                       HTML     49K 
47: R25         Related Party Transactions                          HTML     50K 
48: R26         Geographic Information                              HTML     84K 
49: R27         Selected Quarterly Financial Data                   HTML    106K 
50: R28         Subsequent Events                                   HTML     36K 
51: R29         Summary of Significant Accounting Policies          HTML    209K 
                (Policies)                                                       
52: R30         Summary of Significant Accounting Policies          HTML     64K 
                (Tables)                                                         
53: R31         Acquisitions (Tables)                               HTML    128K 
54: R32         Consolidation (Tables)                              HTML     95K 
55: R33         Investment Securities (Tables)                      HTML    563K 
56: R34         Goodwill and Intangible Assets (Tables)             HTML    117K 
57: R35         Equity Method Investments (Tables)                  HTML     48K 
58: R36         Fair Value Measurements (Tables)                    HTML    438K 
59: R37         Debt (Tables)                                       HTML     83K 
60: R38         Income Taxes (Tables)                               HTML    293K 
61: R39         Other Financial Statement Captions (Tables)         HTML    117K 
62: R40         Noncontrolling Interests (Tables)                   HTML    111K 
63: R41         Long-Term Incentive Compensation (Tables)           HTML    516K 
64: R42         Retirement Benefit Plans (Tables)                   HTML    299K 
65: R43         Accumulated Other Comprehensive Loss (Tables)       HTML    193K 
66: R44         Earnings and Dividends Per Share (Tables)           HTML    124K 
67: R45         Commitments and Contingencies (Tables)              HTML     48K 
68: R46         Related Party Transactions (Tables)                 HTML     46K 
69: R47         Geographic Information (Tables)                     HTML     84K 
70: R48         Selected Quarterly Financial Data (Tables)          HTML    106K 
71: R49         Summary of Significant Accounting Policies -        HTML     67K 
                Consolidation, Property, Equipment and Software,                 
                Deferred Commissions (Details)                                   
72: R50         Summary of Significant Accounting Policies -        HTML     63K 
                Financial Instruments (Details)                                  
73: R51         Summary of Significant Accounting Policies - Stock  HTML     73K 
                Based Compensation, Common Stock (Details)                       
74: R52         Recent Accounting Pronouncements (Details)          HTML     37K 
75: R53         Acquisitions - Merger with JCG (Details)            HTML    123K 
76: R54         Acquisitions - Merger with JCG - Intangible Assets  HTML     58K 
                (Details)                                                        
77: R55         Acquisitions - Merger with JCG - Debt (Details)     HTML     53K 
78: R56         Acquisitions - Merger with JCG - Pro Forma Results  HTML     42K 
                of Operations (Details)                                          
79: R57         Acquisitions - Merger with JCG - Options (Details)  HTML     42K 
80: R58         Consolidation - VIEs (Details)                      HTML     51K 
81: R59         Consolidation - VREs (Details)                      HTML     48K 
82: R60         Investment Securities - General Disclosure          HTML    163K 
                (Details)                                                        
83: R61         Investment Securities - Offsetting Derivatives      HTML    168K 
                (Details)                                                        
84: R62         Goodwill and Intangible Assets (Details)            HTML    107K 
85: R63         Equity Method Investments (Details)                 HTML     60K 
86: R64         Fair Value Measurements - Level of Fair Value       HTML    169K 
                (Details)                                                        
87: R65         Fair Value Measurements - Disposal of Volantis      HTML     43K 
                (Details)                                                        
88: R66         Fair Value Measurements - Acquisition of Geneva     HTML     47K 
                (Details)                                                        
89: R67         Fair Value Measurements - Acquisition of Perennial  HTML     45K 
                (Details)                                                        
90: R68         Fair Value Measurements - Acquisition of Kapstream  HTML     55K 
                (Details)                                                        
91: R69         Fair Value Measurements - Acquisition of            HTML     44K 
                VelocityShares (Details)                                         
92: R70         Fair Value Measurements - Dai-ichi Options          HTML     34K 
                (Details)                                                        
93: R71         Fair Value Measurements - Level 3 Rollforward       HTML    106K 
                (Details)                                                        
94: R72         Fair Value Measurements - Transfers Between Levels  HTML     34K 
                (Details)                                                        
95: R73         Debt (Details)                                      HTML    129K 
96: R74         Income Taxes (Details)                              HTML    128K 
97: R75         Income Taxes - Deferred Taxes (Details)             HTML     80K 
98: R76         Income Taxes - Unrecognized Tax Benefits (Details)  HTML     53K 
99: R77         Other Financial Statement Captions (Details)        HTML     91K 
100: R78         Other Financial Statement Captions - Leases         HTML     37K  
                (Details)                                                        
101: R79         Noncontrolling Interests - Redeemable (Details)     HTML     62K  
102: R80         Noncontrolling Interests - Nonredeemable (Details)  HTML     37K  
103: R81         Long-Term Incentive Compensation - (Details)        HTML    231K  
104: R82         Long-Term Incentive Compensation - Compensation     HTML    335K  
                Plans (Details)                                                  
105: R83         Long-Term Incentive Compensation - ESOP and RSA     HTML    137K  
                (Details)                                                        
106: R84         Retirement benefit plans (Details)                  HTML     52K  
107: R85         Retirement benefit plans - Change in plan assets    HTML    110K  
                and benefit obligations, net retirement benefit                  
                recognized in balance sheet, assumptions (Details)               
108: R86         Retirement benefit plans - Plan assets (Details)    HTML     76K  
109: R87         Retirement benefit plans - Actuarial                HTML    106K  
                gains(Losses), Benefit Cost, Cash Flows (Details)                
110: R88         Accumulated Other Comprehensive Loss (Details)      HTML     62K  
111: R89         Accumulated Other Comprehensive Loss - OCI          HTML     51K  
                (Details)                                                        
112: R90         Earnings and Dividends Per Share (Details)          HTML     79K  
113: R91         Commitments and Contingencies (Details)             HTML     49K  
114: R92         Related Party Transactions (Details)                HTML     47K  
115: R93         Geographic Information (Details)                    HTML     59K  
116: R94         Selected Quarterly Financial Data (Details)         HTML     56K  
117: R95         Subsequent Events (Details)                         HTML     59K  
119: XML         IDEA XML File -- Filing Summary                      XML    204K  
118: EXCEL       IDEA Workbook of Financial Reports                  XLSX    162K  
17: EX-101.INS  XBRL Instance -- jhg-20171231                        XML   8.54M 
19: EX-101.CAL  XBRL Calculations -- jhg-20171231_cal                XML    345K 
21: EX-101.DEF  XBRL Definitions -- jhg-20171231_def                 XML   1.59M 
20: EX-101.LAB  XBRL Labels -- jhg-20171231_lab                      XML   3.08M 
22: EX-101.PRE  XBRL Presentations -- jhg-20171231_pre               XML   2.12M 
18: EX-101.SCH  XBRL Schema -- jhg-20171231                          XSD    418K 
120: ZIP         XBRL Zipped Folder -- 0001047469-18-001112-xbrl      Zip    451K  


‘EX-101.DEF’   —   XBRL Definitions — jhg-20171231_def


This Exhibit is an XBRL XML File.


                                                                                                                                                                                
<?xml version="1.0" encoding="windows-1252"?>
<!-- Created by Merrill Corporation -->
<!-- XBRL document created with Merrill Bridge 7.3.329.0 -->
<!-- Based on XBRL 2.1 -->
<!-- Created on: 2/27/2018 11:39:02 AM -->
<!-- Modified on: 2/27/2018 11:39:02 AM -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xlink="http://www.w3.org/1999/xlink">
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#StatementConsolidatedBalanceSheets" roleURI="http://www.janus.com/role/StatementConsolidatedBalanceSheets" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#StatementConsolidatedStatementsOfCashFlows" roleURI="http://www.janus.com/role/StatementConsolidatedStatementsOfCashFlows" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#StatementConsolidatedStatementsOfChangesInEquity" roleURI="http://www.janus.com/role/StatementConsolidatedStatementsOfChangesInEquity" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureInvestmentSecuritiesTables" roleURI="http://www.janus.com/role/DisclosureInvestmentSecuritiesTables" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureLongTermIncentiveCompensationTables" roleURI="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationTables" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesConsolidationPropertyEquipmentAndSoftwareDeferredCommissionsDetails" roleURI="http://www.janus.com/role/DisclosureSummaryOfSignificantAccountingPoliciesConsolidationPropertyEquipmentAndSoftwareDeferredCommissionsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesFinancialInstrumentsDetails" roleURI="http://www.janus.com/role/DisclosureSummaryOfSignificantAccountingPoliciesFinancialInstrumentsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesStockBasedCompensationCommonStockDetails" roleURI="http://www.janus.com/role/DisclosureSummaryOfSignificantAccountingPoliciesStockBasedCompensationCommonStockDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureRecentAccountingPronouncementsDetails" roleURI="http://www.janus.com/role/DisclosureRecentAccountingPronouncementsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureAcquisitionsMergerWithJcgDetails" roleURI="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureAcquisitionsMergerWithJcgIntangibleAssetsDetails" roleURI="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgIntangibleAssetsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureAcquisitionsMergerWithJcgDebtDetails" roleURI="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgDebtDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureAcquisitionsMergerWithJcgOptionsDetails" roleURI="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgOptionsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureConsolidationViesDetails" roleURI="http://www.janus.com/role/DisclosureConsolidationViesDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureConsolidationVresDetails" roleURI="http://www.janus.com/role/DisclosureConsolidationVresDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureInvestmentSecuritiesGeneralDisclosureDetails" roleURI="http://www.janus.com/role/DisclosureInvestmentSecuritiesGeneralDisclosureDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureInvestmentSecuritiesOffsettingDerivativesDetails" roleURI="http://www.janus.com/role/DisclosureInvestmentSecuritiesOffsettingDerivativesDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureGoodwillAndIntangibleAssetsDetails" roleURI="http://www.janus.com/role/DisclosureGoodwillAndIntangibleAssetsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureEquityMethodInvestmentsDetails" roleURI="http://www.janus.com/role/DisclosureEquityMethodInvestmentsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsLevelOfFairValueDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsLevelOfFairValueDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsDisposalOfVolantisDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsDisposalOfVolantisDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsAcquisitionOfGenevaDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfGenevaDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsAcquisitionOfPerennialDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfPerennialDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsAcquisitionOfKapstreamDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfKapstreamDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsAcquisitionOfVelocitysharesDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfVelocitysharesDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsDaiIchiOptionsDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsDaiIchiOptionsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureFairValueMeasurementsLevel3RollforwardDetails" roleURI="http://www.janus.com/role/DisclosureFairValueMeasurementsLevel3RollforwardDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureDebtDetails" roleURI="http://www.janus.com/role/DisclosureDebtDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureIncomeTaxesDetails" roleURI="http://www.janus.com/role/DisclosureIncomeTaxesDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureIncomeTaxesDeferredTaxesDetails" roleURI="http://www.janus.com/role/DisclosureIncomeTaxesDeferredTaxesDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureOtherFinancialStatementCaptionsDetails" roleURI="http://www.janus.com/role/DisclosureOtherFinancialStatementCaptionsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureOtherFinancialStatementCaptionsLeasesDetails" roleURI="http://www.janus.com/role/DisclosureOtherFinancialStatementCaptionsLeasesDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureNoncontrollingInterestsRedeemableDetails" roleURI="http://www.janus.com/role/DisclosureNoncontrollingInterestsRedeemableDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureNoncontrollingInterestsNonredeemableDetails" roleURI="http://www.janus.com/role/DisclosureNoncontrollingInterestsNonredeemableDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureLongTermIncentiveCompensationDetails" roleURI="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureLongTermIncentiveCompensationCompensationPlansDetails" roleURI="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationCompensationPlansDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureLongTermIncentiveCompensationEsopAndRsaDetails" roleURI="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationEsopAndRsaDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureRetirementBenefitPlansDetails" roleURI="http://www.janus.com/role/DisclosureRetirementBenefitPlansDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureRetirementBenefitPlansChangeInPlanAssetsAndBenefitObligationsNetRetirementBenefitRecognizedInBalanceSheetAssumptionsDetails" roleURI="http://www.janus.com/role/DisclosureRetirementBenefitPlansChangeInPlanAssetsAndBenefitObligationsNetRetirementBenefitRecognizedInBalanceSheetAssumptionsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureRetirementBenefitPlansPlanAssetsDetails" roleURI="http://www.janus.com/role/DisclosureRetirementBenefitPlansPlanAssetsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureRetirementBenefitPlansActuarialGainsLossesBenefitCostCashFlowsDetails" roleURI="http://www.janus.com/role/DisclosureRetirementBenefitPlansActuarialGainsLossesBenefitCostCashFlowsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureAccumulatedOtherComprehensiveLossDetails" roleURI="http://www.janus.com/role/DisclosureAccumulatedOtherComprehensiveLossDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureAccumulatedOtherComprehensiveLossOciDetails" roleURI="http://www.janus.com/role/DisclosureAccumulatedOtherComprehensiveLossOciDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureEarningsAndDividendsPerShareDetails" roleURI="http://www.janus.com/role/DisclosureEarningsAndDividendsPerShareDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureRelatedPartyTransactionsDetails" roleURI="http://www.janus.com/role/DisclosureRelatedPartyTransactionsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureGeographicInformationDetails" roleURI="http://www.janus.com/role/DisclosureGeographicInformationDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<roleRef xlink:type="simple" xlink:href="jhg-20171231.xsd#DisclosureSubsequentEventsDetails" roleURI="http://www.janus.com/role/DisclosureSubsequentEventsDetails" xmlns="http://www.xbrl.org/2003/linkbase"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
<definitionLink xlink:role="http://www.janus.com/role/StatementConsolidatedBalanceSheets" xlink:type="extended" xlink:title="00100 - Statement - CONSOLIDATED BALANCE SHEETS" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain_636553283340695430"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain_636553283340695430" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="us-gaap_ConsolidatedEntitiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_ConsolidatedEntitiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain_636553283340695430"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain_636553283340695430" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember" xlink:label="us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsCurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" xlink:label="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FeesAndOtherReceivablesCurrent" xlink:label="jhg_FeesAndOtherReceivablesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="jhg_FeesAndOtherReceivablesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OEICAndUnitTrustReceivables" xlink:label="jhg_OEICAndUnitTrustReceivables"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="jhg_OEICAndUnitTrustReceivables" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="us-gaap_OtherAssetsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_OtherAssetsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsNoncurrentAbstract" xlink:label="us-gaap_AssetsNoncurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsNoncurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AssetsNoncurrentAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AssetsNoncurrentAbstract" xlink:to="us-gaap_IntangibleAssetsNetExcludingGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AssetsNoncurrentAbstract" xlink:to="us-gaap_Goodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PostEmploymentBenefitsAssetNoncurrent" xlink:label="jhg_PostEmploymentBenefitsAssetNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AssetsNoncurrentAbstract" xlink:to="jhg_PostEmploymentBenefitsAssetNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AssetsNoncurrentAbstract" xlink:to="us-gaap_OtherAssetsNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_Assets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent" xlink:label="us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_EmployeeRelatedLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="us-gaap_LongTermDebtCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LongTermDebtCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OEICAndUnitTrustPayables" xlink:label="jhg_OEICAndUnitTrustPayables"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="jhg_OEICAndUnitTrustPayables" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesNoncurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EmployeeRelatedLiabilitiesNoncurrent" xlink:label="jhg_EmployeeRelatedLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="jhg_EmployeeRelatedLiabilitiesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="us-gaap_LongTermDebtNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_LongTermDebtNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxLiabilitiesNoncurrent" xlink:label="us-gaap_DeferredTaxLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_DeferredTaxLiabilitiesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PostemploymentBenefitsLiabilityNoncurrent" xlink:label="us-gaap_PostemploymentBenefitsLiabilityNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_PostemploymentBenefitsLiabilityNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="us-gaap_OtherLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_OtherLiabilitiesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_Liabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_CommitmentsAndContingencies" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityFairValue" xlink:label="us-gaap_RedeemableNoncontrollingInterestEquityFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_RedeemableNoncontrollingInterestEquityFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:label="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_CommonStockValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_AdditionalPaidInCapital" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockValue" xlink:label="us-gaap_TreasuryStockValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_TreasuryStockValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_StockholdersEquity" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonredeemableNoncontrollingInterest" xlink:label="us-gaap_NonredeemableNoncontrollingInterest"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_NonredeemableNoncontrollingInterest" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:to="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/StatementConsolidatedStatementsOfCashFlows" xlink:type="extended" xlink:title="00300 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="us-gaap_ConsolidatedEntitiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_ConsolidatedEntitiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember" xlink:label="us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProfitLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="us-gaap_DepreciationDepletionAndAmortization"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DepreciationDepletionAndAmortization" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DeferredIncomeTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ShareBasedCompensation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromEquityMethodInvestments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_IncomeLossFromEquityMethodInvestments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestments" xlink:label="us-gaap_GainLossOnInvestments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_GainLossOnInvestments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PensionContributionsInExcessOfPensionCostsRecognized" xlink:label="jhg_PensionContributionsInExcessOfPensionCostsRecognized"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="jhg_PensionContributionsInExcessOfPensionCostsRecognized" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncashIncomeExpense" xlink:label="us-gaap_OtherNoncashIncomeExpense"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_OtherNoncashIncomeExpense" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IncreaseDecreaseInOEICAndUnitTrustReceivablesAndPayables" xlink:label="jhg_IncreaseDecreaseInOEICAndUnitTrustReceivablesAndPayables"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="jhg_IncreaseDecreaseInOEICAndUnitTrustReceivablesAndPayables" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOtherOperatingAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IncreaseDecreaseInOtherAccrualsAndLiabilities" xlink:label="jhg_IncreaseDecreaseInOtherAccrualsAndLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="jhg_IncreaseDecreaseInOtherAccrualsAndLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAcquiredFromAcquisition" xlink:label="us-gaap_CashAcquiredFromAcquisition"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_CashAcquiredFromAcquisition" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries" xlink:label="us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestmentsAbstract" xlink:label="us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestmentsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestmentsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromInvestmentSecuritiesVariableInterestEntitiesNet" xlink:label="jhg_ProceedsFromInvestmentSecuritiesVariableInterestEntitiesNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestmentsAbstract" xlink:to="jhg_ProceedsFromInvestmentSecuritiesVariableInterestEntitiesNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromInvestmentSecuritiesSeedCapitalNet" xlink:label="jhg_ProceedsFromInvestmentSecuritiesSeedCapitalNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestmentsAbstract" xlink:to="jhg_ProceedsFromInvestmentSecuritiesSeedCapitalNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireProductiveAssetsAbstract" xlink:label="us-gaap_PaymentsToAcquireProductiveAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireProductiveAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PurchasesSettlementsAndMaturitiesOfMarketableSecuritiesAndDerivatives" xlink:label="jhg_PurchasesSettlementsAndMaturitiesOfMarketableSecuritiesAndDerivatives"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PaymentsToAcquireProductiveAssetsAbstract" xlink:to="jhg_PurchasesSettlementsAndMaturitiesOfMarketableSecuritiesAndDerivatives" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PaymentsToAcquireProductiveAssetsAbstract" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PaymentsToAcquireProductiveAssetsAbstract" xlink:to="us-gaap_PaymentsToAcquireIntangibleAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromInvestmentIncomeReceivedByConsolidatedFunds" xlink:label="jhg_ProceedsFromInvestmentIncomeReceivedByConsolidatedFunds"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="jhg_ProceedsFromInvestmentIncomeReceivedByConsolidatedFunds" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashDivestedFromDeconsolidation" xlink:label="us-gaap_CashDivestedFromDeconsolidation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_CashDivestedFromDeconsolidation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForProceedsFromHedgeInvestingActivities" xlink:label="us-gaap_PaymentsForProceedsFromHedgeInvestingActivities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsForProceedsFromHedgeInvestingActivities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital" xlink:label="us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DividendsAttributableToNoncontrollingInterests" xlink:label="jhg_DividendsAttributableToNoncontrollingInterests"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="jhg_DividendsAttributableToNoncontrollingInterests" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleOfEquityMethodInvestments" xlink:label="us-gaap_ProceedsFromSaleOfEquityMethodInvestments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfEquityMethodInvestments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromVolantis" xlink:label="jhg_ProceedsFromVolantis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="jhg_ProceedsFromVolantis" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromSettlementOfConvertibleNoteHedge" xlink:label="jhg_ProceedsFromSettlementOfConvertibleNoteHedge"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="jhg_ProceedsFromSettlementOfConvertibleNoteHedge" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PaymentsForSettlementOfStockWarrant" xlink:label="jhg_PaymentsForSettlementOfStockWarrant"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="jhg_PaymentsForSettlementOfStockWarrant" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="us-gaap_ProceedsFromStockOptionsExercised"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromStockOptionsExercised" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromStockPlans" xlink:label="us-gaap_ProceedsFromStockPlans"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromStockPlans" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PaymentsForRepurchaseOfCommonStockForStockBasedCompensationPlans" xlink:label="jhg_PaymentsForRepurchaseOfCommonStockForStockBasedCompensationPlans"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="jhg_PaymentsForRepurchaseOfCommonStockForStockBasedCompensationPlans" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock" xlink:label="us-gaap_PaymentsOfDividendsCommonStock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfDividendsCommonStock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="us-gaap_RepaymentsOfLongTermDebt"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_RepaymentsOfLongTermDebt" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfDividendsMinorityInterest" xlink:label="us-gaap_PaymentsOfDividendsMinorityInterest"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfDividendsMinorityInterest" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromThirdPartyInvestmentsInSeededInvestmentProductsNetOfRedemptions" xlink:label="jhg_ProceedsFromThirdPartyInvestmentsInSeededInvestmentProductsNetOfRedemptions"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="jhg_ProceedsFromThirdPartyInvestmentsInSeededInvestmentProductsNetOfRedemptions" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents" xlink:label="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract" xlink:to="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestPaidNet" xlink:label="us-gaap_InterestPaidNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_InterestPaidNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="us-gaap_IncomeTaxesPaidNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_IncomeTaxesPaidNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ReconciliationOfCashAndCashEquivalentsAbstract" xlink:label="jhg_ReconciliationOfCashAndCashEquivalentsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseAbstract" xlink:to="jhg_ReconciliationOfCashAndCashEquivalentsAbstract" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/StatementConsolidatedStatementsOfChangesInEquity" xlink:type="extended" xlink:title="00400 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_636553283340885449"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_636553283340885449" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="us-gaap_TreasuryStockMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_TreasuryStockMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="us-gaap_NoncontrollingInterestMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_NoncontrollingInterestMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_CommonStockSharesOutstanding" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockSplits" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockSplits"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockSplits" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NetIncomeLossExcludingRedeemableNoncontrollingInterests" xlink:label="jhg_NetIncomeLossExcludingRedeemableNoncontrollingInterests"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_NetIncomeLossExcludingRedeemableNoncontrollingInterests" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="us-gaap_DividendsCommonStockCash"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_DividendsCommonStockCash" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders" xlink:label="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AdjustmentsToAdditionalPaidInCapitalDerivativeInstrumentsAcquired" xlink:label="jhg_AdjustmentsToAdditionalPaidInCapitalDerivativeInstrumentsAcquired"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_AdjustmentsToAdditionalPaidInCapitalDerivativeInstrumentsAcquired" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination" xlink:label="us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueAdjustmentsToRedeemableNoncontrollingInterests" xlink:label="jhg_FairValueAdjustmentsToRedeemableNoncontrollingInterests"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_FairValueAdjustmentsToRedeemableNoncontrollingInterests" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AdjustConsiderationForPostCombinationServicesUnderUnvestedStockBasedCompensationPlans" xlink:label="jhg_AdjustConsiderationForPostCombinationServicesUnderUnvestedStockBasedCompensationPlans"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_AdjustConsiderationForPostCombinationServicesUnderUnvestedStockBasedCompensationPlans" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AdjustmentsToAdditionalPaidInCapitalDerivativeInstrumentsSettlement" xlink:label="jhg_AdjustmentsToAdditionalPaidInCapitalDerivativeInstrumentsSettlement"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_AdjustmentsToAdditionalPaidInCapitalDerivativeInstrumentsSettlement" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AdjustmentsToAdditionalPaidInCapitalTaxImpactResultingFromSettlementOfDerivativeInstruments" xlink:label="jhg_AdjustmentsToAdditionalPaidInCapitalTaxImpactResultingFromSettlementOfDerivativeInstruments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_AdjustmentsToAdditionalPaidInCapitalTaxImpactResultingFromSettlementOfDerivativeInstruments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockRepurchasedForStockBasedCompensationPlanDuringPeriodValue" xlink:label="jhg_StockRepurchasedForStockBasedCompensationPlanDuringPeriodValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_StockRepurchasedForStockBasedCompensationPlanDuringPeriodValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AdjustmentsToAdditionalPaidInCapitalRedenominationAndReductionOfParValue" xlink:label="jhg_AdjustmentsToAdditionalPaidInCapitalRedenominationAndReductionOfParValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_AdjustmentsToAdditionalPaidInCapitalRedenominationAndReductionOfParValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VestingOfStockBasedCompensationPlansValue" xlink:label="jhg_VestingOfStockBasedCompensationPlansValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_VestingOfStockBasedCompensationPlansValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockIssuedForStockBasedCompensationPlansDuringPeriodValue" xlink:label="jhg_StockIssuedForStockBasedCompensationPlansDuringPeriodValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_StockIssuedForStockBasedCompensationPlansDuringPeriodValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockIssuedForStockBasedCompensationPlansDuringPeriodShares" xlink:label="jhg_StockIssuedForStockBasedCompensationPlansDuringPeriodShares"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="jhg_StockIssuedForStockBasedCompensationPlansDuringPeriodShares" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="21" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="22" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedDuringPeriodValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="23" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockRepurchasedDuringPeriodValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="24" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockRepurchasedDuringPeriodShares" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureInvestmentSecuritiesTables" xlink:type="extended" xlink:title="30603 - Disclosure - Investment Securities (Tables)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="us-gaap_HedgingDesignationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_HedgingDesignationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain_636553283340925453"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain_636553283340925453" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NotDesignatedAsHedgingInstrumentTradingMember" xlink:label="us-gaap_NotDesignatedAsHedgingInstrumentTradingMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_NotDesignatedAsHedgingInstrumentTradingMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentSecondaryCategorizationAxis" xlink:label="us-gaap_InvestmentSecondaryCategorizationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_InvestmentSecondaryCategorizationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:label="us-gaap_InvestmentsBySecondaryCategorizationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentSecondaryCategorizationAxis" xlink:to="us-gaap_InvestmentsBySecondaryCategorizationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:label="us-gaap_InvestmentsBySecondaryCategorizationDomain_636553283340925453"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_InvestmentSecondaryCategorizationAxis" xlink:to="us-gaap_InvestmentsBySecondaryCategorizationDomain_636553283340925453" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeededInvestmentProductsMember" xlink:label="jhg_SeededInvestmentProductsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeededInvestmentProductsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentTableTextBlock" xlink:label="invest_InvestmentTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="invest_InvestmentTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ScheduleOfRealizedGainLossOnTradingSecuritiesTableTextBlock" xlink:label="jhg_ScheduleOfRealizedGainLossOnTradingSecuritiesTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_ScheduleOfRealizedGainLossOnTradingSecuritiesTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock" xlink:label="us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OffsettingAssetsAndLiabilitiesTableTextBlock" xlink:label="jhg_OffsettingAssetsAndLiabilitiesTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_OffsettingAssetsAndLiabilitiesTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ScheduleOfDerivativeInstrumentsDenominatedInForeignCurrencyGainsLossesInStatementOfFinancialPerformanceTextBlock" xlink:label="jhg_ScheduleOfDerivativeInstrumentsDenominatedInForeignCurrencyGainsLossesInStatementOfFinancialPerformanceTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_ScheduleOfDerivativeInstrumentsDenominatedInForeignCurrencyGainsLossesInStatementOfFinancialPerformanceTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OffsettingAssetsAndLiabilitiesWithinSeededInvestmentProductsTableTextBlock" xlink:label="jhg_OffsettingAssetsAndLiabilitiesWithinSeededInvestmentProductsTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_OffsettingAssetsAndLiabilitiesWithinSeededInvestmentProductsTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsTextBlock" xlink:label="us-gaap_GainLossOnInvestmentsTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_GainLossOnInvestmentsTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsTableTextBlock" xlink:label="jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsTableTextBlock" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationTables" xlink:type="extended" xlink:title="31403 - Disclosure - Long-Term Incentive Compensation (Tables)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AwardTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_636553283340935454"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_636553283340935454" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockAppreciationRightsSARSMember" xlink:label="us-gaap_StockAppreciationRightsSARSMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_StockAppreciationRightsSARSMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockAppreciationRightsSarsInOctober2014Member" xlink:label="jhg_StockAppreciationRightsSarsInOctober2014Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockAppreciationRightsSARSMember" xlink:to="jhg_StockAppreciationRightsSarsInOctober2014Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_PlanNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain_636553283340945455"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain_636553283340945455" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LongtermIncentivePlanMember" xlink:label="jhg_LongtermIncentivePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_LongtermIncentivePlanMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredEquityPlanMember" xlink:label="jhg_DeferredEquityPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_DeferredEquityPlanMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ScheduleOfAssumptionsUsedForFairValueOfStockAppreciationRightsTableTextBlock" xlink:label="jhg_ScheduleOfAssumptionsUsedForFairValueOfStockAppreciationRightsTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_ScheduleOfAssumptionsUsedForFairValueOfStockAppreciationRightsTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardWeightedTableTextBlock" xlink:label="jhg_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardWeightedTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardWeightedTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock" xlink:label="us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGrantDateIntrinsicValueTableTextBlock" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGrantDateIntrinsicValueTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGrantDateIntrinsicValueTableTextBlock" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfNonvestedShareActivityTableTextBlock" xlink:label="us-gaap_ScheduleOfNonvestedShareActivityTableTextBlock"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ScheduleOfNonvestedShareActivityTableTextBlock" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureSummaryOfSignificantAccountingPoliciesConsolidationPropertyEquipmentAndSoftwareDeferredCommissionsDetails" xlink:type="extended" xlink:title="40201 - Disclosure - Summary of Significant Accounting Policies - Consolidation, Property, Equipment and Software, Deferred Commissions (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain_636553283340965457"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain_636553283340965457" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FurnitureFixturesAndEquipmentIncludingComputerEquipmentAndSystemsMember" xlink:label="jhg_FurnitureFixturesAndEquipmentIncludingComputerEquipmentAndSystemsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="jhg_FurnitureFixturesAndEquipmentIncludingComputerEquipmentAndSystemsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="us-gaap_LeaseholdImprovementsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_LeaseholdImprovementsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="us-gaap_ComputerEquipmentMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_ComputerEquipmentMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember_636553283340965457"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember_636553283340965457" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MinimumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="us-gaap_DepreciationAndAmortization"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_DepreciationAndAmortization" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentUsefulLife" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentDepreciationMethods" xlink:label="us-gaap_PropertyPlantAndEquipmentDepreciationMethods"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentDepreciationMethods" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="us-gaap_PropertyPlantAndEquipmentGross"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentGross" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse" xlink:label="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredCostsAbstract" xlink:label="us-gaap_DeferredCostsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_DeferredCostsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PeriodOverWhichSalesCommissionsCanBeDeferredAndAmortizedMaximum" xlink:label="jhg_PeriodOverWhichSalesCommissionsCanBeDeferredAndAmortizedMaximum"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DeferredCostsAbstract" xlink:to="jhg_PeriodOverWhichSalesCommissionsCanBeDeferredAndAmortizedMaximum" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureSummaryOfSignificantAccountingPoliciesFinancialInstrumentsDetails" xlink:type="extended" xlink:title="40202 - Disclosure - Summary of Significant Accounting Policies - Financial Instruments (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:label="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MinimumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeAxis" xlink:label="us-gaap_InvestmentTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:to="us-gaap_InvestmentTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="us-gaap_InvestmentTypeCategorizationMember_636553283340985459"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember_636553283340985459" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MutualFundMember" xlink:label="us-gaap_MutualFundMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="us-gaap_MutualFundMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="us-gaap_DerivativeLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PercentageOfOwnershipInterestInInvestmentProduct" xlink:label="jhg_PercentageOfOwnershipInterestInInvestmentProduct"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeLineItems" xlink:to="jhg_PercentageOfOwnershipInterestInInvestmentProduct" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer" xlink:label="us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetImpairmentCharges" xlink:label="us-gaap_AssetImpairmentCharges"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_AssetImpairmentCharges" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_TradeAndOtherReceivablesPaymentTerms" xlink:label="jhg_TradeAndOtherReceivablesPaymentTerms"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeLineItems" xlink:to="jhg_TradeAndOtherReceivablesPaymentTerms" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRecognitionAbstract" xlink:label="us-gaap_RevenueRecognitionAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_RevenueRecognitionAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NumberOfComponentsInvolvedInInvestmentAdvisoryFeePayment" xlink:label="jhg_NumberOfComponentsInvolvedInInvestmentAdvisoryFeePayment"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RevenueRecognitionAbstract" xlink:to="jhg_NumberOfComponentsInvolvedInInvestmentAdvisoryFeePayment" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PerformanceFeeAdjustmentVariableRate" xlink:label="jhg_PerformanceFeeAdjustmentVariableRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RevenueRecognitionAbstract" xlink:to="jhg_PerformanceFeeAdjustmentVariableRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PerformanceFeeAdjustmentMeasurementPeriod" xlink:label="jhg_PerformanceFeeAdjustmentMeasurementPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RevenueRecognitionAbstract" xlink:to="jhg_PerformanceFeeAdjustmentMeasurementPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PerformanceFeeAdjustmentUltimateMeasurementPeriod" xlink:label="jhg_PerformanceFeeAdjustmentUltimateMeasurementPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_RevenueRecognitionAbstract" xlink:to="jhg_PerformanceFeeAdjustmentUltimateMeasurementPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityAbstract" xlink:label="us-gaap_EquityAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_EquityAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityAbstract" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureSummaryOfSignificantAccountingPoliciesStockBasedCompensationCommonStockDetails" xlink:type="extended" xlink:title="40203 - Disclosure - Summary of Significant Accounting Policies - Stock Based Compensation, Common Stock (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BasisOfPresentationTable" xlink:label="jhg_BasisOfPresentationTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="jhg_BasisOfPresentationTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="jhg_BasisOfPresentationTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_636553283340995460"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_636553283340995460" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="us-gaap_CustomerRelationshipsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_CustomerRelationshipsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BasisOfPresentationLineItems" xlink:label="jhg_BasisOfPresentationLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="jhg_BasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromStockPlans" xlink:label="us-gaap_ProceedsFromStockPlans"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_ProceedsFromStockPlans" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AccumulatedShareBasedCompensationCosts" xlink:label="jhg_AccumulatedShareBasedCompensationCosts"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="jhg_AccumulatedShareBasedCompensationCosts" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetUsefulLife" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NumberOfReportingUnits" xlink:label="us-gaap_NumberOfReportingUnits"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_NumberOfReportingUnits" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_GainLossRecognizedOnPurchaseIssueSaleOrCancellationOfOwnEquityShares" xlink:label="jhg_GainLossRecognizedOnPurchaseIssueSaleOrCancellationOfOwnEquityShares"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="jhg_GainLossRecognizedOnPurchaseIssueSaleOrCancellationOfOwnEquityShares" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_CommonStockSharesIssued" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_CommonStockValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_AdditionalPaidInCapital" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AdjustmentsToAdditionalPaidInCapitalChangeInParValue" xlink:label="jhg_AdjustmentsToAdditionalPaidInCapitalChangeInParValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="jhg_AdjustmentsToAdditionalPaidInCapitalChangeInParValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="jhg_BasisOfPresentationLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureRecentAccountingPronouncementsDetails" xlink:type="extended" xlink:title="40301 - Disclosure - Recent Accounting Pronouncements (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember_636553283341005461"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember_636553283341005461" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AccountingStandardsUpdates201608Member" xlink:label="jhg_AccountingStandardsUpdates201608Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="jhg_AccountingStandardsUpdates201608Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AccountingStandardsUpdate201707Member" xlink:label="jhg_AccountingStandardsUpdate201707Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="jhg_AccountingStandardsUpdate201707Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IncreaseInAnnualRevenueDueToChangeInPresentationOfDistributionFees" xlink:label="jhg_IncreaseInAnnualRevenueDueToChangeInPresentationOfDistributionFees"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="jhg_IncreaseInAnnualRevenueDueToChangeInPresentationOfDistributionFees" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ReclassificationOfOtherComponentsOfNetPeriodicPensionCostsPresentedOutsideOfOperations" xlink:label="jhg_ReclassificationOfOtherComponentsOfNetPeriodicPensionCostsPresentedOutsideOfOperations"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:to="jhg_ReclassificationOfOtherComponentsOfNetPeriodicPensionCostsPresentedOutsideOfOperations" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgDetails" xlink:type="extended" xlink:title="40401 - Disclosure - Acquisitions - Merger with JCG (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain_636553283341015462"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_636553283341015462" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_HendersonGroupPLCMember" xlink:label="jhg_HendersonGroupPLCMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="jhg_HendersonGroupPLCMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_636553283341015462"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain_636553283341015462" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_JanusCapitalGroupIncMember" xlink:label="jhg_JanusCapitalGroupIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_JanusCapitalGroupIncMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NumberOfShareReceivedInConnectionWithMergerAgreement" xlink:label="jhg_NumberOfShareReceivedInConnectionWithMergerAgreement"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_NumberOfShareReceivedInConnectionWithMergerAgreement" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionSharePrice" xlink:label="us-gaap_BusinessAcquisitionSharePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessAcquisitionSharePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract" xlink:label="jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PreliminaryPurchasePriceOfGoodwill" xlink:label="jhg_PreliminaryPurchasePriceOfGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract" xlink:to="jhg_PreliminaryPurchasePriceOfGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationPreliminaryPurchasePriceOfDeferredTaxLiabilities" xlink:label="jhg_BusinessCombinationPreliminaryPurchasePriceOfDeferredTaxLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract" xlink:to="jhg_BusinessCombinationPreliminaryPurchasePriceOfDeferredTaxLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationPreliminaryPurchasePriceOfOtherNonCurrentLiabilities" xlink:label="jhg_BusinessCombinationPreliminaryPurchasePriceOfOtherNonCurrentLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract" xlink:to="jhg_BusinessCombinationPreliminaryPurchasePriceOfOtherNonCurrentLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationFairValueOfNoncontrollingInterestIncludedInPreliminaryPurchasePrice" xlink:label="jhg_BusinessCombinationFairValueOfNoncontrollingInterestIncludedInPreliminaryPurchasePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract" xlink:to="jhg_BusinessCombinationFairValueOfNoncontrollingInterestIncludedInPreliminaryPurchasePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationPreliminaryPurchasePriceOfRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="jhg_BusinessCombinationPreliminaryPurchasePriceOfRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_BusinessCombinationPreliminaryAllocationOfPurchasePriceToRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAbstract" xlink:to="jhg_BusinessCombinationPreliminaryPurchasePriceOfRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract" xlink:label="us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments" xlink:label="us-gaap_GoodwillPurchaseAccountingAdjustments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract" xlink:to="us-gaap_GoodwillPurchaseAccountingAdjustments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities" xlink:label="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract" xlink:to="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherNonCurrentLiabilities" xlink:label="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherNonCurrentLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract" xlink:to="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherNonCurrentLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentNoncontrollingInterests" xlink:label="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentNoncontrollingInterests"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract" xlink:to="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentNoncontrollingInterests" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetsNet" xlink:label="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetsNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract" xlink:to="jhg_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetsNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_Goodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayableAndAccruedLiabilities" xlink:label="jhg_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayableAndAccruedLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="jhg_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayableAndAccruedLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue" xlink:label="us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgIntangibleAssetsDetails" xlink:type="extended" xlink:title="40402 - Disclosure - Acquisitions - Merger with JCG - Intangible Assets (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LegacyJanusMember" xlink:label="jhg_LegacyJanusMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="jhg_LegacyJanusMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_JanusCapitalGroupIncMember" xlink:label="jhg_JanusCapitalGroupIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_JanusCapitalGroupIncMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_636553283341075468"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_636553283341075468" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MutualFundMember" xlink:label="us-gaap_MutualFundMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_MutualFundMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ExchangeTradedFundsMember" xlink:label="us-gaap_ExchangeTradedFundsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_ExchangeTradedFundsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_InvestmentManagementAgreementsMember" xlink:label="jhg_InvestmentManagementAgreementsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="jhg_InvestmentManagementAgreementsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TrademarksMember" xlink:label="us-gaap_TrademarksMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_TrademarksMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeparatelyManagedAccountsMember" xlink:label="jhg_SeparatelyManagedAccountsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="jhg_SeparatelyManagedAccountsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_InvestmentManagementContractsExchangeTradedNotesMember" xlink:label="jhg_InvestmentManagementContractsExchangeTradedNotesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="jhg_InvestmentManagementContractsExchangeTradedNotesMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwillAbstract" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwillAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwillAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwillAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwillAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwillAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwillAbstract" xlink:to="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgDebtDetails" xlink:type="extended" xlink:title="40403 - Disclosure - Acquisitions - Merger with JCG - Debt (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_JanusCapitalGroupIncMember" xlink:label="jhg_JanusCapitalGroupIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_JanusCapitalGroupIncMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_DebtInstrumentAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain_636553283341085469"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain_636553283341085469" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ConvertibleSeniorNotes0.750PercentDue2018Member" xlink:label="jhg_ConvertibleSeniorNotes0.750PercentDue2018Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="jhg_ConvertibleSeniorNotes0.750PercentDue2018Member" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeniorNotes4.875PercentDue2025Member" xlink:label="jhg_SeniorNotes4.875PercentDue2025Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="jhg_SeniorNotes4.875PercentDue2025Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DebtInstrumentConvertibleCarryingAmountOfLiabilityComponent" xlink:label="jhg_DebtInstrumentConvertibleCarryingAmountOfLiabilityComponent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_DebtInstrumentConvertibleCarryingAmountOfLiabilityComponent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DebtInstrumentConvertibleDiscountedCashFlowPercentage" xlink:label="jhg_DebtInstrumentConvertibleDiscountedCashFlowPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_DebtInstrumentConvertibleDiscountedCashFlowPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent" xlink:label="us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentFairValue" xlink:label="us-gaap_DebtInstrumentFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_DebtInstrumentFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentUnamortizedPremium" xlink:label="us-gaap_DebtInstrumentUnamortizedPremium"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_DebtInstrumentUnamortizedPremium" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureAcquisitionsMergerWithJcgOptionsDetails" xlink:type="extended" xlink:title="40405 - Disclosure - Acquisitions - Merger with JCG - Options (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="us-gaap_CounterpartyNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_CounterpartyNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="us-gaap_RepurchaseAgreementCounterpartyNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_CounterpartyNameAxis" xlink:to="us-gaap_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="us-gaap_RepurchaseAgreementCounterpartyNameDomain_636553283341105471"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_CounterpartyNameAxis" xlink:to="us-gaap_RepurchaseAgreementCounterpartyNameDomain_636553283341105471" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DaiichiLifeHoldingsIncMember" xlink:label="jhg_DaiichiLifeHoldingsIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="jhg_DaiichiLifeHoldingsIncMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NumberOfTranches" xlink:label="jhg_NumberOfTranches"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_NumberOfTranches" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ConditionalOptionsTrancheNumberOfShares" xlink:label="jhg_ConditionalOptionsTrancheNumberOfShares"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_ConditionalOptionsTrancheNumberOfShares" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StrikePrice" xlink:label="jhg_StrikePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_StrikePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OptionsSoldConsideration" xlink:label="jhg_OptionsSoldConsideration"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_OptionsSoldConsideration" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeNet" xlink:label="us-gaap_DerivativeFairValueOfDerivativeNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_DerivativeFairValueOfDerivativeNet" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureConsolidationViesDetails" xlink:type="extended" xlink:title="40501 - Disclosure - Consolidation - VIEs (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" xlink:label="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="us-gaap_OtherAssetsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherAssetsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet" xlink:label="us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RedeemableNoncontrollingInterestInVariableInterestEntity" xlink:label="jhg_RedeemableNoncontrollingInterestInVariableInterestEntity"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_RedeemableNoncontrollingInterestInVariableInterestEntity" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NonredeemableNoncontrollingInterestInVariableInterestEntity" xlink:label="jhg_NonredeemableNoncontrollingInterestInVariableInterestEntity"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_NonredeemableNoncontrollingInterestInVariableInterestEntity" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VariableInterestEntityConsolidatedAssetsAndLiabilitiesExcludingNoncontrollingInterestNet" xlink:label="jhg_VariableInterestEntityConsolidatedAssetsAndLiabilitiesExcludingNoncontrollingInterestNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_VariableInterestEntityConsolidatedAssetsAndLiabilitiesExcludingNoncontrollingInterestNet" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureConsolidationVresDetails" xlink:type="extended" xlink:title="40502 - Disclosure - Consolidation - VREs (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VariableRightsEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="jhg_VariableRightsEntityNotPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="jhg_VariableRightsEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" xlink:label="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="us-gaap_OtherAssetsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherAssetsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VotingRightsEntitiesConsolidatedCarryingAmountAssetsAndLiabilitiesNet" xlink:label="jhg_VotingRightsEntitiesConsolidatedCarryingAmountAssetsAndLiabilitiesNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_VotingRightsEntitiesConsolidatedCarryingAmountAssetsAndLiabilitiesNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RedeemableNoncontrollingInterestInVotingRightsEntities" xlink:label="jhg_RedeemableNoncontrollingInterestInVotingRightsEntities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_RedeemableNoncontrollingInterestInVotingRightsEntities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VotingRightsEntitiesConsolidatedAssetsAndLiabilitiesExcludingNoncontrollingInterestNet" xlink:label="jhg_VotingRightsEntitiesConsolidatedAssetsAndLiabilitiesExcludingNoncontrollingInterestNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_VotingRightsEntitiesConsolidatedAssetsAndLiabilitiesExcludingNoncontrollingInterestNet" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureInvestmentSecuritiesGeneralDisclosureDetails" xlink:type="extended" xlink:title="40601 - Disclosure - Investment Securities - General Disclosure (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentTable" xlink:label="invest_InvestmentTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="invest_InvestmentTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain_636553283341125473"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain_636553283341125473" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FutureMember" xlink:label="us-gaap_FutureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_FutureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDefaultSwapMember" xlink:label="us-gaap_CreditDefaultSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_CreditDefaultSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IndexSwapMember" xlink:label="jhg_IndexSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="jhg_IndexSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TotalReturnSwapMember" xlink:label="us-gaap_TotalReturnSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_TotalReturnSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ForeignExchangeForwardMember" xlink:label="us-gaap_ForeignExchangeForwardMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForeignExchangeForwardMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="us-gaap_ConsolidatedEntitiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="invest_InvestmentTable" xlink:to="us-gaap_ConsolidatedEntitiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeMember" xlink:label="us-gaap_EquityMethodInvesteeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_EquityMethodInvesteeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesMember" xlink:label="us-gaap_ConsolidatedEntitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_ConsolidatedEntitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="invest_InvestmentTable" xlink:to="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:label="us-gaap_GainLossOnInvestmentsByCategoryAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="invest_InvestmentTable" xlink:to="us-gaap_GainLossOnInvestmentsByCategoryAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:label="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:to="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:label="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain_636553283341135474"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:to="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain_636553283341135474" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TradingAccountAssetsMember" xlink:label="us-gaap_TradingAccountAssetsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="us-gaap_TradingAccountAssetsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableforsaleSecuritiesMember" xlink:label="us-gaap_AvailableforsaleSecuritiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="us-gaap_AvailableforsaleSecuritiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DerivativeInstrumentsMember" xlink:label="jhg_DerivativeInstrumentsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="jhg_DerivativeInstrumentsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDerivativesByContractTypeAxis" xlink:label="us-gaap_CreditDerivativesByContractTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="invest_InvestmentTable" xlink:to="us-gaap_CreditDerivativesByContractTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDerivativesContractTypeDomain" xlink:label="us-gaap_CreditDerivativesContractTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_CreditDerivativesByContractTypeAxis" xlink:to="us-gaap_CreditDerivativesContractTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDerivativesContractTypeDomain" xlink:label="us-gaap_CreditDerivativesContractTypeDomain_636553283341145475"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_CreditDerivativesByContractTypeAxis" xlink:to="us-gaap_CreditDerivativesContractTypeDomain_636553283341145475" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDefaultSwapSellingProtectionMember" xlink:label="us-gaap_CreditDefaultSwapSellingProtectionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CreditDerivativesContractTypeDomain" xlink:to="us-gaap_CreditDefaultSwapSellingProtectionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentSecondaryCategorizationAxis" xlink:label="us-gaap_InvestmentSecondaryCategorizationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="6" xlink:from="invest_InvestmentTable" xlink:to="us-gaap_InvestmentSecondaryCategorizationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:label="us-gaap_InvestmentsBySecondaryCategorizationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentSecondaryCategorizationAxis" xlink:to="us-gaap_InvestmentsBySecondaryCategorizationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeededInvestmentProductsMember" xlink:label="jhg_SeededInvestmentProductsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeededInvestmentProductsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeparatelyManagedAccountsMember" xlink:label="jhg_SeparatelyManagedAccountsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeparatelyManagedAccountsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PooledInvestmentFundsMember" xlink:label="jhg_PooledInvestmentFundsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_PooledInvestmentFundsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredCompensationHedgeAssetMember" xlink:label="jhg_DeferredCompensationHedgeAssetMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_DeferredCompensationHedgeAssetMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherInvestmentsMember" xlink:label="us-gaap_OtherInvestmentsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="us-gaap_OtherInvestmentsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingDesignationAxis" xlink:label="us-gaap_HedgingDesignationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="7" xlink:from="invest_InvestmentTable" xlink:to="us-gaap_HedgingDesignationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NotDesignatedAsHedgingInstrumentTradingMember" xlink:label="us-gaap_NotDesignatedAsHedgingInstrumentTradingMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_NotDesignatedAsHedgingInstrumentTradingMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentLineItems" xlink:label="invest_InvestmentLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="invest_InvestmentLineItems" xlink:to="invest_InvestmentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermInvestmentsAbstract" xlink:label="us-gaap_ShortTermInvestmentsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="invest_InvestmentLineItems" xlink:to="us-gaap_ShortTermInvestmentsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_InvestmentInSeededInvestmentProducts" xlink:label="jhg_InvestmentInSeededInvestmentProducts"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="jhg_InvestmentInSeededInvestmentProducts" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentOwnedAtFairValue" xlink:label="us-gaap_InvestmentOwnedAtFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="us-gaap_InvestmentOwnedAtFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss" xlink:label="us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainLossAbstract" xlink:label="us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainLossAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="invest_InvestmentLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainLossAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAmortizedCost" xlink:label="us-gaap_AvailableForSaleSecuritiesAmortizedCost"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainLossAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesAmortizedCost" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainLossAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ForeignCurrencyTranslationGainLoss" xlink:label="jhg_ForeignCurrencyTranslationGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainLossAbstract" xlink:to="jhg_ForeignCurrencyTranslationGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="us-gaap_AvailableForSaleSecurities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainLossAbstract" xlink:to="us-gaap_AvailableForSaleSecurities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="invest_DerivativeNotionalAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="invest_InvestmentLineItems" xlink:to="invest_DerivativeNotionalAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OffsettingDerivativeAssetsAbstract" xlink:label="us-gaap_OffsettingDerivativeAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="invest_InvestmentLineItems" xlink:to="us-gaap_OffsettingDerivativeAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeFairValueOfDerivativeAsset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetFairValueGrossLiability" xlink:label="us-gaap_DerivativeAssetFairValueGrossLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeAssetFairValueGrossLiability" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset" xlink:label="us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="us-gaap_DerivativeAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:label="us-gaap_OffsettingDerivativeLiabilitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="invest_InvestmentLineItems" xlink:to="us-gaap_OffsettingDerivativeLiabilitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeFairValueOfDerivativeLiability" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:label="us-gaap_DerivativeLiabilityFairValueGrossAsset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeLiabilityFairValueGrossAsset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset" xlink:label="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" xlink:label="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="invest_InvestmentLineItems" xlink:to="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossRealized"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" xlink:to="us-gaap_ForeignCurrencyTransactionGainLossRealized" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainsLossesNetDenominatedInForeignCurrency" xlink:label="jhg_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainsLossesNetDenominatedInForeignCurrency"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" xlink:to="jhg_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainsLossesNetDenominatedInForeignCurrency" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_GainsLossesOnDerivativeInstrumentsHeldForTradingPurposesNetDenominatedInForeignCurrency" xlink:label="jhg_GainsLossesOnDerivativeInstrumentsHeldForTradingPurposesNetDenominatedInForeignCurrency"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" xlink:to="jhg_GainsLossesOnDerivativeInstrumentsHeldForTradingPurposesNetDenominatedInForeignCurrency" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureInvestmentSecuritiesOffsettingDerivativesDetails" xlink:type="extended" xlink:title="40602 - Disclosure - Investment Securities - Offsetting Derivatives (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OffsettingAssetsAndLiabilitiesTable" xlink:label="jhg_OffsettingAssetsAndLiabilitiesTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:label="us-gaap_GainLossOnInvestmentsByCategoryAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="jhg_OffsettingAssetsAndLiabilitiesTable" xlink:to="us-gaap_GainLossOnInvestmentsByCategoryAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:label="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:to="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TradingAccountAssetsMember" xlink:label="us-gaap_TradingAccountAssetsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="us-gaap_TradingAccountAssetsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableforsaleSecuritiesMember" xlink:label="us-gaap_AvailableforsaleSecuritiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="us-gaap_AvailableforsaleSecuritiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DerivativeInstrumentsMember" xlink:label="jhg_DerivativeInstrumentsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="jhg_DerivativeInstrumentsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentSecondaryCategorizationAxis" xlink:label="us-gaap_InvestmentSecondaryCategorizationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="jhg_OffsettingAssetsAndLiabilitiesTable" xlink:to="us-gaap_InvestmentSecondaryCategorizationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:label="us-gaap_InvestmentsBySecondaryCategorizationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentSecondaryCategorizationAxis" xlink:to="us-gaap_InvestmentsBySecondaryCategorizationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeededInvestmentProductsMember" xlink:label="jhg_SeededInvestmentProductsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeededInvestmentProductsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMovementOnDerivativesMember" xlink:label="jhg_FairValueMovementOnDerivativesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_FairValueMovementOnDerivativesMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvestmentsMember" xlink:label="us-gaap_EquityMethodInvestmentsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="us-gaap_EquityMethodInvestmentsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SaleOfVolantisMember" xlink:label="jhg_SaleOfVolantisMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SaleOfVolantisMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherInvestmentsMember" xlink:label="us-gaap_OtherInvestmentsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="us-gaap_OtherInvestmentsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="us-gaap_ConsolidatedEntitiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="jhg_OffsettingAssetsAndLiabilitiesTable" xlink:to="us-gaap_ConsolidatedEntitiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesMember" xlink:label="us-gaap_ConsolidatedEntitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_ConsolidatedEntitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDerivativesByContractTypeAxis" xlink:label="us-gaap_CreditDerivativesByContractTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="jhg_OffsettingAssetsAndLiabilitiesTable" xlink:to="us-gaap_CreditDerivativesByContractTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDerivativesContractTypeDomain" xlink:label="us-gaap_CreditDerivativesContractTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_CreditDerivativesByContractTypeAxis" xlink:to="us-gaap_CreditDerivativesContractTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDefaultSwapSellingProtectionMember" xlink:label="us-gaap_CreditDefaultSwapSellingProtectionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CreditDerivativesContractTypeDomain" xlink:to="us-gaap_CreditDefaultSwapSellingProtectionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="jhg_OffsettingAssetsAndLiabilitiesTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MinimumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="6" xlink:from="jhg_OffsettingAssetsAndLiabilitiesTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FutureMember" xlink:label="us-gaap_FutureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_FutureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ContractsForDifferencesMember" xlink:label="jhg_ContractsForDifferencesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="jhg_ContractsForDifferencesMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IndexSwapMember" xlink:label="jhg_IndexSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="jhg_IndexSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TotalReturnSwapMember" xlink:label="us-gaap_TotalReturnSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_TotalReturnSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDefaultSwapMember" xlink:label="us-gaap_CreditDefaultSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_CreditDefaultSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PutOptionMember" xlink:label="us-gaap_PutOptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_PutOptionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SwapMember" xlink:label="us-gaap_SwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_SwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ForeignExchangeForwardMember" xlink:label="us-gaap_ForeignExchangeForwardMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForeignExchangeForwardMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OffsettingAssetsAndLiabilitiesLineItems" xlink:label="jhg_OffsettingAssetsAndLiabilitiesLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="jhg_OffsettingAssetsAndLiabilitiesLineItems" xlink:to="jhg_OffsettingAssetsAndLiabilitiesTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OffsettingDerivativeAssetsAbstract" xlink:label="us-gaap_OffsettingDerivativeAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_OffsettingAssetsAndLiabilitiesLineItems" xlink:to="us-gaap_OffsettingDerivativeAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeFairValueOfDerivativeAsset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetFairValueGrossLiability" xlink:label="us-gaap_DerivativeAssetFairValueGrossLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeAssetFairValueGrossLiability" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset" xlink:label="us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="us-gaap_DerivativeAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_OffsettingDerivativeAssetsAbstract" xlink:to="us-gaap_DerivativeAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:label="us-gaap_OffsettingDerivativeLiabilitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_OffsettingAssetsAndLiabilitiesLineItems" xlink:to="us-gaap_OffsettingDerivativeLiabilitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeFairValueOfDerivativeLiability" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:label="us-gaap_DerivativeLiabilityFairValueGrossAsset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeLiabilityFairValueGrossAsset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset" xlink:label="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_OffsettingDerivativeLiabilitiesAbstract" xlink:to="us-gaap_DerivativeLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SummaryOfCreditDerivativesAbstract" xlink:label="us-gaap_SummaryOfCreditDerivativesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_OffsettingAssetsAndLiabilitiesLineItems" xlink:to="us-gaap_SummaryOfCreditDerivativesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDerivativeTerm1" xlink:label="us-gaap_CreditDerivativeTerm1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SummaryOfCreditDerivativesAbstract" xlink:to="us-gaap_CreditDerivativeTerm1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="invest_DerivativeNotionalAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SummaryOfCreditDerivativesAbstract" xlink:to="invest_DerivativeNotionalAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditRiskDerivativesAtFairValueNet" xlink:label="us-gaap_CreditRiskDerivativesAtFairValueNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SummaryOfCreditDerivativesAbstract" xlink:to="us-gaap_CreditRiskDerivativesAtFairValueNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" xlink:label="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_OffsettingAssetsAndLiabilitiesLineItems" xlink:to="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestments" xlink:label="us-gaap_GainLossOnInvestments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_DerivativeInstrumentDenominatedInForeignCurrencyAbstract" xlink:to="us-gaap_GainLossOnInvestments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsAbstract" xlink:label="jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_OffsettingAssetsAndLiabilitiesLineItems" xlink:to="jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PurchasesSettlementsAndMaturitiesOfMarketableSecuritiesAndDerivatives" xlink:label="jhg_PurchasesSettlementsAndMaturitiesOfMarketableSecuritiesAndDerivatives"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsAbstract" xlink:to="jhg_PurchasesSettlementsAndMaturitiesOfMarketableSecuritiesAndDerivatives" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromSalesSettlementsOrMaturitiesOfMarketableSecuritiesAndDerivatives" xlink:label="jhg_ProceedsFromSalesSettlementsOrMaturitiesOfMarketableSecuritiesAndDerivatives"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_CashFlowsRelatedToInvestmentSecuritiesAndOtherAssetsAbstract" xlink:to="jhg_ProceedsFromSalesSettlementsOrMaturitiesOfMarketableSecuritiesAndDerivatives" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureGoodwillAndIntangibleAssetsDetails" xlink:type="extended" xlink:title="40701 - Disclosure - Goodwill and Intangible Assets (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ScheduleOfIntangibleAssetsAndGoodwillTable" xlink:label="jhg_ScheduleOfIntangibleAssetsAndGoodwillTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillTable" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_InvestmentManagementAgreementsMember" xlink:label="jhg_InvestmentManagementAgreementsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="jhg_InvestmentManagementAgreementsMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TrademarksMember" xlink:label="us-gaap_TrademarksMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_TrademarksMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="us-gaap_CustomerRelationshipsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_CustomerRelationshipsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems" xlink:label="jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems" xlink:to="jhg_ScheduleOfIntangibleAssetsAndGoodwillTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsRollForward" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_IndefiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:label="us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_IndefiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:label="us-gaap_FiniteLivedIntangibleAssetsRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_FiniteLivedIntangibleAssetsGross" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss" xlink:label="us-gaap_FiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_FiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="us-gaap_AmortizationOfIntangibleAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_AmortizationOfIntangibleAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AccumulatedAmortizationRelatedToForeignCurrencyTranslationGainLoss" xlink:label="jhg_AccumulatedAmortizationRelatedToForeignCurrencyTranslationGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:to="jhg_AccumulatedAmortizationRelatedToForeignCurrencyTranslationGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FiniteLivedIntangibleAssetsRollForward" xlink:to="us-gaap_FiniteLivedIntangibleAssetUsefulLife" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IntangibleAssetsNetExcludingGoodwillRollForward" xlink:label="jhg_IntangibleAssetsNetExcludingGoodwillRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems" xlink:to="jhg_IntangibleAssetsNetExcludingGoodwillRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_IntangibleAssetsNetExcludingGoodwillRollForward" xlink:to="us-gaap_IntangibleAssetsNetExcludingGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_IntangibleAssetsNetExcludingGoodwillRollForward" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IntangibleAssetsTranslationAdjustments" xlink:label="jhg_IntangibleAssetsTranslationAdjustments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_IntangibleAssetsNetExcludingGoodwillRollForward" xlink:to="jhg_IntangibleAssetsTranslationAdjustments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillRollForward" xlink:label="us-gaap_GoodwillRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems" xlink:to="us-gaap_GoodwillRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_GoodwillRollForward" xlink:to="us-gaap_Goodwill" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillAcquiredDuringPeriod" xlink:label="us-gaap_GoodwillAcquiredDuringPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_GoodwillRollForward" xlink:to="us-gaap_GoodwillAcquiredDuringPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss" xlink:label="us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_GoodwillRollForward" xlink:to="us-gaap_GoodwillForeignCurrencyTranslationGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GoodwillImpairmentLoss" xlink:label="us-gaap_GoodwillImpairmentLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_GoodwillRollForward" xlink:to="us-gaap_GoodwillImpairmentLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:label="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_ScheduleOfIntangibleAssetsAndGoodwillLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureEquityMethodInvestmentsDetails" xlink:type="extended" xlink:title="40801 - Disclosure - Equity Method Investments (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable" xlink:label="us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsTable" xlink:to="us-gaap_BalanceSheetLocationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain_636553283341385499"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain_636553283341385499" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember" xlink:label="us-gaap_OtherNoncurrentAssetsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherNoncurrentAssetsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsTable" xlink:to="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="us-gaap_EquityMethodInvesteeNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="us-gaap_EquityMethodInvesteeNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="us-gaap_EquityMethodInvesteeNameDomain_636553283341385499"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="us-gaap_EquityMethodInvesteeNameDomain_636553283341385499" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LongTailAlphaMember" xlink:label="jhg_LongTailAlphaMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityMethodInvesteeNameDomain" xlink:to="jhg_LongTailAlphaMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OptimumInvestmentManagementLimitedMember" xlink:label="jhg_OptimumInvestmentManagementLimitedMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EquityMethodInvesteeNameDomain" xlink:to="jhg_OptimumInvestmentManagementLimitedMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NorthernPinesGroupsMember" xlink:label="jhg_NorthernPinesGroupsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EquityMethodInvesteeNameDomain" xlink:to="jhg_NorthernPinesGroupsMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NorthernPinesHendersonCapitalGpLLCMember" xlink:label="jhg_NorthernPinesHendersonCapitalGpLLCMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_NorthernPinesGroupsMember" xlink:to="jhg_NorthernPinesHendersonCapitalGpLLCMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NorthernPinesHendersonCapitalLLCMember" xlink:label="jhg_NorthernPinesHendersonCapitalLLCMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_NorthernPinesGroupsMember" xlink:to="jhg_NorthernPinesHendersonCapitalLLCMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:label="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:to="us-gaap_ScheduleOfEquityMethodInvestmentsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvestments" xlink:label="us-gaap_EquityMethodInvestments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:label="us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentOwnershipPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvestmentDividendsOrDistributions" xlink:label="us-gaap_EquityMethodInvestmentDividendsOrDistributions"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:to="us-gaap_EquityMethodInvestmentDividendsOrDistributions" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EquityMethodInvestmentSummarizedFinancialInformationImpairmentLoss" xlink:label="jhg_EquityMethodInvestmentSummarizedFinancialInformationImpairmentLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:to="jhg_EquityMethodInvestmentSummarizedFinancialInformationImpairmentLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromEquityMethodInvestments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:to="us-gaap_IncomeLossFromEquityMethodInvestments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleOfEquityMethodInvestments" xlink:label="us-gaap_ProceedsFromSaleOfEquityMethodInvestments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:to="us-gaap_ProceedsFromSaleOfEquityMethodInvestments" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsLevelOfFairValueDetails" xlink:type="extended" xlink:title="40901 - Disclosure - Fair Value Measurements - Level of Fair Value (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_636553283341395500"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_636553283341395500" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="us-gaap_ConsolidatedEntitiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_ConsolidatedEntitiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IntechFoundersMember" xlink:label="jhg_IntechFoundersMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="jhg_IntechFoundersMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesMember" xlink:label="us-gaap_ConsolidatedEntitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_ConsolidatedEntitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="jhg_VariableRightsEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VariableRightsEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="jhg_VariableRightsEntityNotPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="jhg_VariableRightsEntityNotPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_636553283341405501"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_636553283341405501" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:label="us-gaap_GainLossOnInvestmentsByCategoryAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_GainLossOnInvestmentsByCategoryAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:label="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:to="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TradingAccountAssetsMember" xlink:label="us-gaap_TradingAccountAssetsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="us-gaap_TradingAccountAssetsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableforsaleSecuritiesMember" xlink:label="us-gaap_AvailableforsaleSecuritiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="us-gaap_AvailableforsaleSecuritiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentSecondaryCategorizationAxis" xlink:label="us-gaap_InvestmentSecondaryCategorizationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="6" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_InvestmentSecondaryCategorizationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:label="us-gaap_InvestmentsBySecondaryCategorizationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentSecondaryCategorizationAxis" xlink:to="us-gaap_InvestmentsBySecondaryCategorizationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SecuritiesInvestmentMember" xlink:label="us-gaap_SecuritiesInvestmentMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="us-gaap_SecuritiesInvestmentMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeededHedgeDerivatesMember" xlink:label="jhg_SeededHedgeDerivatesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeededHedgeDerivatesMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeededInvestmentProductsMember" xlink:label="jhg_SeededInvestmentProductsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeededInvestmentProductsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="7" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FutureMember" xlink:label="us-gaap_FutureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_FutureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredBonusesHedgeLiabilityMember" xlink:label="jhg_DeferredBonusesHedgeLiabilityMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="jhg_DeferredBonusesHedgeLiabilityMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DaiIchiOptionMember" xlink:label="jhg_DaiIchiOptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="jhg_DaiIchiOptionMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IndexSwapMember" xlink:label="jhg_IndexSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="jhg_IndexSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TotalReturnSwapMember" xlink:label="us-gaap_TotalReturnSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_TotalReturnSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ForeignExchangeForwardMember" xlink:label="us-gaap_ForeignExchangeForwardMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForeignExchangeForwardMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditDefaultSwapMember" xlink:label="us-gaap_CreditDefaultSwapMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_CreditDefaultSwapMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:label="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_CashAndCashEquivalentsFairValueDisclosure" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" xlink:label="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="us-gaap_DerivativeAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DerivativeAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationAsset" xlink:label="us-gaap_BusinessCombinationContingentConsiderationAsset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_BusinessCombinationContingentConsiderationAsset" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="us-gaap_AssetsFairValueDisclosure"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_AssetsFairValueDisclosure" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:label="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DerivativeLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FinancialLiabilitiesFairValueDisclosure" xlink:label="us-gaap_FinancialLiabilitiesFairValueDisclosure"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_FinancialLiabilitiesFairValueDisclosure" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LongTermDebtCurrentFairValue" xlink:label="jhg_LongTermDebtCurrentFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="jhg_LongTermDebtCurrentFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtFairValue" xlink:label="us-gaap_LongTermDebtFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_LongTermDebtFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure" xlink:label="us-gaap_LiabilitiesFairValueDisclosure"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_LiabilitiesFairValueDisclosure" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityFairValue" xlink:label="us-gaap_RedeemableNoncontrollingInterestEquityFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_RedeemableNoncontrollingInterestEquityFairValue" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsDisposalOfVolantisDetails" xlink:type="extended" xlink:title="40902 - Disclosure - Fair Value Measurements - Disposal of Volantis (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_636553283341465507"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_636553283341465507" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VolantisMember" xlink:label="jhg_VolantisMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:to="jhg_VolantisMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupClassificationAxis" xlink:label="us-gaap_DisposalGroupClassificationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:to="us-gaap_DisposalGroupClassificationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:label="us-gaap_DisposalGroupClassificationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:label="us-gaap_DisposalGroupClassificationDomain_636553283341465507"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationDomain_636553283341465507" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:label="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DisposalGroupClassificationDomain" xlink:to="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ConsiderationForSaleBasedOnRevenueOfInvesteePercentage" xlink:label="jhg_ConsiderationForSaleBasedOnRevenueOfInvesteePercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="jhg_ConsiderationForSaleBasedOnRevenueOfInvesteePercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PeriodOfPerformanceOfInvesteeForRecognizingConsideration" xlink:label="jhg_PeriodOfPerformanceOfInvesteeForRecognizingConsideration"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="jhg_PeriodOfPerformanceOfInvesteeForRecognizingConsideration" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsDiscountRate" xlink:label="us-gaap_FairValueInputsDiscountRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_FairValueInputsDiscountRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationAsset" xlink:label="us-gaap_BusinessCombinationContingentConsiderationAsset"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationAsset" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfGenevaDetails" xlink:type="extended" xlink:title="40903 - Disclosure - Fair Value Measurements - Acquisition of Geneva (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_GenevaCapitalManagementLLCMember" xlink:label="jhg_GenevaCapitalManagementLLCMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_GenevaCapitalManagementLLCMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationNumberOfPaymentTranches" xlink:label="jhg_BusinessCombinationContingentConsiderationNumberOfPaymentTranches"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationNumberOfPaymentTranches" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationPayableInFirstTranche" xlink:label="jhg_BusinessCombinationContingentConsiderationPayableInFirstTranche"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationPayableInFirstTranche" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationPayableInSecondTranche" xlink:label="jhg_BusinessCombinationContingentConsiderationPayableInSecondTranche"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationPayableInSecondTranche" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationArrangementsPaymentPeriod" xlink:label="jhg_BusinessCombinationContingentConsiderationArrangementsPaymentPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationArrangementsPaymentPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfPerennialDetails" xlink:type="extended" xlink:title="40904 - Disclosure - Fair Value Measurements - Acquisition of Perennial (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PerennialFixedInterestPartnersPtyLtdAndPerennialGrowthManagementPtyLtdMember" xlink:label="jhg_PerennialFixedInterestPartnersPtyLtdAndPerennialGrowthManagementPtyLtdMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_PerennialFixedInterestPartnersPtyLtdAndPerennialGrowthManagementPtyLtdMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BalanceSheetLocationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember" xlink:label="us-gaap_OtherNoncurrentLiabilitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherNoncurrentLiabilitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInTheRangeOfOutcomesContingentConsiderationLiabilityValueHigh" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInTheRangeOfOutcomesContingentConsiderationLiabilityValueHigh"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInTheRangeOfOutcomesContingentConsiderationLiabilityValueHigh" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationArrangementsChangeInRangeOfOutcomesContingentConsiderationAdditionalLiabilityValueHigh" xlink:label="jhg_BusinessCombinationContingentConsiderationArrangementsChangeInRangeOfOutcomesContingentConsiderationAdditionalLiabilityValueHigh"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationArrangementsChangeInRangeOfOutcomesContingentConsiderationAdditionalLiabilityValueHigh" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationNumberOfPaymentTranches" xlink:label="jhg_BusinessCombinationContingentConsiderationNumberOfPaymentTranches"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationNumberOfPaymentTranches" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfKapstreamDetails" xlink:type="extended" xlink:title="40905 - Disclosure - Fair Value Measurements - Acquisition of Kapstream (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_KapstreamCapitalPtyLimitedMember" xlink:label="jhg_KapstreamCapitalPtyLimitedMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_KapstreamCapitalPtyLimitedMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BalanceSheetLocationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesMember" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember" xlink:label="us-gaap_OtherNoncurrentLiabilitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherNoncurrentLiabilitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:label="us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesPeriodLow" xlink:label="jhg_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesPeriodLow"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesPeriodLow" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesPeriodHigh" xlink:label="jhg_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesPeriodHigh"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesPeriodHigh" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NumberOfInstallmentsForConsiderationPayable" xlink:label="jhg_NumberOfInstallmentsForConsiderationPayable"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="jhg_NumberOfInstallmentsForConsiderationPayable" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsAcquisitionOfVelocitysharesDetails" xlink:type="extended" xlink:title="40906 - Disclosure - Fair Value Measurements - Acquisition of VelocityShares (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VelocitysharesLLCMember" xlink:label="jhg_VelocitysharesLLCMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_VelocitysharesLLCMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ContingentConsiderationPeriodicPaymentAxis" xlink:label="jhg_ContingentConsiderationPeriodicPaymentAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="jhg_ContingentConsiderationPeriodicPaymentAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ContingentConsiderationPeriodicPaymentDomain" xlink:label="jhg_ContingentConsiderationPeriodicPaymentDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="jhg_ContingentConsiderationPeriodicPaymentAxis" xlink:to="jhg_ContingentConsiderationPeriodicPaymentDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ContingentConsiderationPeriodicPaymentDomain" xlink:label="jhg_ContingentConsiderationPeriodicPaymentDomain_636553283341515512"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="jhg_ContingentConsiderationPeriodicPaymentAxis" xlink:to="jhg_ContingentConsiderationPeriodicPaymentDomain_636553283341515512" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ThirdAnniversaryMember" xlink:label="jhg_ThirdAnniversaryMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_ContingentConsiderationPeriodicPaymentDomain" xlink:to="jhg_ThirdAnniversaryMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FourthAnniversaryMember" xlink:label="jhg_FourthAnniversaryMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_ContingentConsiderationPeriodicPaymentDomain" xlink:to="jhg_FourthAnniversaryMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BalanceSheetLocationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesMember" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember" xlink:label="us-gaap_OtherNoncurrentLiabilitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherNoncurrentLiabilitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsDaiIchiOptionsDetails" xlink:type="extended" xlink:title="40907 - Disclosure - Fair Value Measurements - Dai-ichi Options (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="us-gaap_CounterpartyNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:to="us-gaap_CounterpartyNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="us-gaap_RepurchaseAgreementCounterpartyNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_CounterpartyNameAxis" xlink:to="us-gaap_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DaiichiLifeHoldingsIncMember" xlink:label="jhg_DaiichiLifeHoldingsIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="jhg_DaiichiLifeHoldingsIncMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeNet" xlink:label="us-gaap_DerivativeFairValueOfDerivativeNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_DerivativeFairValueOfDerivativeNet" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureFairValueMeasurementsLevel3RollforwardDetails" xlink:type="extended" xlink:title="40908 - Disclosure - Fair Value Measurements - Level 3 Rollforward (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:label="us-gaap_GainLossOnInvestmentsByCategoryAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_GainLossOnInvestmentsByCategoryAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:label="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_GainLossOnInvestmentsByCategoryAxis" xlink:to="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TradingAccountAssetsMember" xlink:label="us-gaap_TradingAccountAssetsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_GainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostCategoriesOfInvestmentsDomain" xlink:to="us-gaap_TradingAccountAssetsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="us-gaap_ClassificationOfVariableInterestEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:to="us-gaap_ClassificationOfVariableInterestEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" xlink:label="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:to="us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueByAssetAndLiabilityClassAxis" xlink:label="jhg_FairValueByAssetAndLiabilityClassAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="jhg_FairValueByAssetAndLiabilityClassAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain" xlink:label="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="jhg_FairValueByAssetAndLiabilityClassAxis" xlink:to="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain" xlink:label="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain_636553283341545515"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="jhg_FairValueByAssetAndLiabilityClassAxis" xlink:to="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain_636553283341545515" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ContingentConsiderationMember" xlink:label="jhg_ContingentConsiderationMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain" xlink:to="jhg_ContingentConsiderationMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredBonusMember" xlink:label="us-gaap_DeferredBonusMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain" xlink:to="us-gaap_DeferredBonusMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DaiIchiOptionMember" xlink:label="jhg_DaiIchiOptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain" xlink:to="jhg_DaiIchiOptionMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RedeemableNonControllingInterestsMember" xlink:label="jhg_RedeemableNonControllingInterestsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetAndLiabilityClassDomain" xlink:to="jhg_RedeemableNonControllingInterestsMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="us-gaap_ValuationTechniqueAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="6" xlink:from="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_ValuationTechniqueAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="us-gaap_ValuationTechniqueDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ValuationTechniqueAxis" xlink:to="us-gaap_ValuationTechniqueDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="us-gaap_ValuationTechniqueDomain_636553283341545515"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_ValuationTechniqueAxis" xlink:to="us-gaap_ValuationTechniqueDomain_636553283341545515" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DiscountedCashFlowMethodMember" xlink:label="jhg_DiscountedCashFlowMethodMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ValuationTechniqueDomain" xlink:to="jhg_DiscountedCashFlowMethodMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="7" xlink:from="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MinimumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageMember" xlink:label="us-gaap_WeightedAverageMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_WeightedAverageMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:label="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAcquiredFromMerger" xlink:label="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAcquiredFromMerger"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAcquiredFromMerger" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchasesSalesIssuancesSettlements" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchasesSalesIssuancesSettlements"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchasesSalesIssuancesSettlements" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityChangesInOwnership" xlink:label="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityChangesInOwnership"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityChangesInOwnership" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityNetMovementInBonusDeferrals" xlink:label="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityNetMovementInBonusDeferrals"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityNetMovementInBonusDeferrals" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAdjustments" xlink:label="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAdjustments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAdjustments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityUnrealizedLoss" xlink:label="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityUnrealizedLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityUnrealizedLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAmortizationOfAppreciationRights" xlink:label="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAmortizationOfAppreciationRights"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAmortizationOfAppreciationRights" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityDistributionsToNonControllingInterestHolders" xlink:label="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityDistributionsToNonControllingInterestHolders"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityDistributionsToNonControllingInterestHolders" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossRealized"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_ForeignCurrencyTransactionGainLossRealized" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" xlink:label="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_MarketableSecuritiesAndDerivativeInstrumentsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsDiscountRate" xlink:label="us-gaap_FairValueInputsDiscountRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueInputsDiscountRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple" xlink:label="us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="us-gaap_FairValueInputsEarningsBeforeInterestTaxesDepreciationAndAmortizationMultiple" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FairValueInputsPriceEarningsRatio" xlink:label="jhg_FairValueInputsPriceEarningsRatio"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="jhg_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward" xlink:to="jhg_FairValueInputsPriceEarningsRatio" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureDebtDetails" xlink:type="extended" xlink:title="41001 - Disclosure - Debt (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_DebtInstrumentAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeniorNotes4.875PercentDue2025Member" xlink:label="jhg_SeniorNotes4.875PercentDue2025Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="jhg_SeniorNotes4.875PercentDue2025Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ConvertibleSeniorNotes0.750PercentDue2018Member" xlink:label="jhg_ConvertibleSeniorNotes0.750PercentDue2018Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="jhg_ConvertibleSeniorNotes0.750PercentDue2018Member" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeniorNotes7.25PercentDue2016Member" xlink:label="jhg_SeniorNotes7.25PercentDue2016Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="jhg_SeniorNotes7.25PercentDue2016Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_UnsecuredRevolvingCreditFacilityMember" xlink:label="jhg_UnsecuredRevolvingCreditFacilityMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="jhg_UnsecuredRevolvingCreditFacilityMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_JanusCapitalGroupIncMember" xlink:label="jhg_JanusCapitalGroupIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="jhg_JanusCapitalGroupIncMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_636553283341595520"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember_636553283341595520" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_CarryingReportedAmountFairValueDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_EstimateOfFairValueFairValueDisclosureMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_DebtInstrumentRedemptionPeriodAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentRedemptionPeriodAxis" xlink:to="us-gaap_DebtInstrumentRedemptionPeriodDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain" xlink:label="us-gaap_DebtInstrumentRedemptionPeriodDomain_636553283341605521"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DebtInstrumentRedemptionPeriodAxis" xlink:to="us-gaap_DebtInstrumentRedemptionPeriodDomain_636553283341605521" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_FirstAnniversaryOnDateOfAgreementMember" xlink:label="jhg_FirstAnniversaryOnDateOfAgreementMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentRedemptionPeriodDomain" xlink:to="jhg_FirstAnniversaryOnDateOfAgreementMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" xlink:label="us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebt" xlink:label="us-gaap_LongTermDebt"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" xlink:to="us-gaap_LongTermDebt" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="us-gaap_LongTermDebtCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" xlink:to="us-gaap_LongTermDebtCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="us-gaap_LongTermDebtNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" xlink:to="us-gaap_LongTermDebtNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:label="us-gaap_LongTermDebtOtherDisclosuresAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebtOtherDisclosuresAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentFaceAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentFairValue" xlink:label="us-gaap_DebtInstrumentFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentUnamortizedPremium" xlink:label="us-gaap_DebtInstrumentUnamortizedPremium"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentUnamortizedPremium" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DebtInstrumentConvertibleCarryingAmountOfLiabilityComponent" xlink:label="jhg_DebtInstrumentConvertibleCarryingAmountOfLiabilityComponent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="jhg_DebtInstrumentConvertibleCarryingAmountOfLiabilityComponent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DebtInstrumentConvertibleDiscountedCashFlowPercentage" xlink:label="jhg_DebtInstrumentConvertibleDiscountedCashFlowPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="jhg_DebtInstrumentConvertibleDiscountedCashFlowPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent" xlink:label="us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1" xlink:label="us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentConvertibleConversionRatio1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:label="us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentConvertibleConversionPrice1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger" xlink:label="us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays" xlink:label="us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentConvertibleThresholdTradingDays" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1" xlink:label="us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DebtInstrumentRedemptionPrincipalAmountRedeemed" xlink:label="jhg_DebtInstrumentRedemptionPrincipalAmountRedeemed"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="jhg_DebtInstrumentRedemptionPrincipalAmountRedeemed" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="us-gaap_RepaymentsOfLongTermDebt"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_RepaymentsOfLongTermDebt" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProceedsFromTerminationOfConvertibleNoteHedge" xlink:label="jhg_ProceedsFromTerminationOfConvertibleNoteHedge"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="jhg_ProceedsFromTerminationOfConvertibleNoteHedge" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForRepurchaseOfWarrants" xlink:label="us-gaap_PaymentsForRepurchaseOfWarrants"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_PaymentsForRepurchaseOfWarrants" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTerm" xlink:label="us-gaap_DebtInstrumentTerm"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_DebtInstrumentTerm" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LineOfCreditFacilityCovenantTermsFinancingLeverageRatioUpperRangeLimit" xlink:label="jhg_LineOfCreditFacilityCovenantTermsFinancingLeverageRatioUpperRangeLimit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="jhg_LineOfCreditFacilityCovenantTermsFinancingLeverageRatioUpperRangeLimit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCredit" xlink:label="us-gaap_LineOfCredit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="us-gaap_LineOfCredit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NumberOfOneYearExtensionOptionAvailableBeforeMaturityPeriod" xlink:label="jhg_NumberOfOneYearExtensionOptionAvailableBeforeMaturityPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="jhg_NumberOfOneYearExtensionOptionAvailableBeforeMaturityPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ExtendedPeriodOfMaturityOnExerciseOfOption" xlink:label="jhg_ExtendedPeriodOfMaturityOnExerciseOfOption"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="21" xlink:from="us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:to="jhg_ExtendedPeriodOfMaturityOnExerciseOfOption" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureIncomeTaxesDetails" xlink:type="extended" xlink:title="41101 - Disclosure - Income Taxes (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="us-gaap_StatementGeographicalAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementGeographicalAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="us-gaap_SegmentGeographicalDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementGeographicalAxis" xlink:to="us-gaap_SegmentGeographicalDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="us-gaap_SegmentGeographicalDomain_636553283341655526"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_StatementGeographicalAxis" xlink:to="us-gaap_SegmentGeographicalDomain_636553283341655526" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_GB" xlink:label="country_GB"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="country_GB" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ForeignExcludingUkMember" xlink:label="jhg_ForeignExcludingUkMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="jhg_ForeignExcludingUkMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:label="us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CurrentForeignTaxExpenseBenefit" xlink:label="us-gaap_CurrentForeignTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="us-gaap_CurrentForeignTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefit" xlink:label="us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="us-gaap_CurrentFederalStateAndLocalTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CurrentIncomeTaxExpenseBenefit" xlink:label="us-gaap_CurrentIncomeTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="us-gaap_CurrentIncomeTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredForeignIncomeTaxExpenseBenefit" xlink:label="us-gaap_DeferredForeignIncomeTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="us-gaap_DeferredForeignIncomeTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredFederalStateAndLocalTaxExpenseBenefit" xlink:label="us-gaap_DeferredFederalStateAndLocalTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="us-gaap_DeferredFederalStateAndLocalTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DeferredIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="us-gaap_DeferredIncomeTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestmentsAbstract" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestmentsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestmentsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestmentsAbstract" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestmentsAbstract" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestmentsAbstract" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationDispositionOfAssets" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationDispositionOfAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationDispositionOfAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EffectiveIncomeTaxRateReconciliationFinalizationOfTaxPositionsPercentage" xlink:label="jhg_EffectiveIncomeTaxRateReconciliationFinalizationOfTaxPositionsPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="jhg_EffectiveIncomeTaxRateReconciliationFinalizationOfTaxPositionsPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationDeductions" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationDeductions"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationDeductions" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseMergerPercentage" xlink:label="jhg_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseMergerPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="jhg_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseMergerPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EffectiveIncomeTaxRateReconciliationBeforeNoncontrollingInterestIncomeLossPercentage" xlink:label="jhg_EffectiveIncomeTaxRateReconciliationBeforeNoncontrollingInterestIncomeLossPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="jhg_EffectiveIncomeTaxRateReconciliationBeforeNoncontrollingInterestIncomeLossPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationMinorityInterestIncomeExpense" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationMinorityInterestIncomeExpense"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationMinorityInterestIncomeExpense" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="us-gaap_EffectiveIncomeTaxRateContinuingOperations" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_TaxCutsAndJobsActOf2017ChangeInTaxRateIncomeTaxExpenseBenefit" xlink:label="jhg_TaxCutsAndJobsActOf2017ChangeInTaxRateIncomeTaxExpenseBenefit"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_TaxCutsAndJobsActOf2017ChangeInTaxRateIncomeTaxExpenseBenefit" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_TaxCutsAndJobsActOf2017IncomeTaxExpenseBenefitIncompleteAccountingProvisionalAmount" xlink:label="jhg_TaxCutsAndJobsActOf2017IncomeTaxExpenseBenefitIncompleteAccountingProvisionalAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_TaxCutsAndJobsActOf2017IncomeTaxExpenseBenefitIncompleteAccountingProvisionalAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_TaxCutsAndJobsActOf2017IncompleteAccountingTransitionTaxForAccumulatedForeignEarningsProvisionalLiability" xlink:label="jhg_TaxCutsAndJobsActOf2017IncompleteAccountingTransitionTaxForAccumulatedForeignEarningsProvisionalLiability"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_TaxCutsAndJobsActOf2017IncompleteAccountingTransitionTaxForAccumulatedForeignEarningsProvisionalLiability" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BenefitFromReductionOfUKCorporationTaxRateInFutureYears" xlink:label="jhg_BenefitFromReductionOfUKCorporationTaxRateInFutureYears"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_BenefitFromReductionOfUKCorporationTaxRateInFutureYears" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EstimatedIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRatePercent" xlink:label="jhg_EstimatedIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRatePercent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_EstimatedIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRatePercent" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureIncomeTaxesDeferredTaxesDetails" xlink:type="extended" xlink:title="41102 - Disclosure - Income Taxes - Deferred Taxes (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_BalanceSheetLocationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember" xlink:label="us-gaap_OtherNoncurrentAssetsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherNoncurrentAssetsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComponentsOfDeferredTaxLiabilitiesAbstract" xlink:label="us-gaap_ComponentsOfDeferredTaxLiabilitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ComponentsOfDeferredTaxLiabilitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:label="us-gaap_ComponentsOfDeferredTaxAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ComponentsOfDeferredTaxLiabilitiesAbstract" xlink:to="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDebtPremium" xlink:label="jhg_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDebtPremium"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="jhg_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsDebtPremium" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsOther" xlink:label="us-gaap_DeferredTaxAssetsOther"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="us-gaap_DeferredTaxAssetsOther" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsGross" xlink:label="us-gaap_DeferredTaxAssetsGross"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="us-gaap_DeferredTaxAssetsGross" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowance" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="us-gaap_DeferredTaxAssetsValuationAllowance" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsNet" xlink:label="us-gaap_DeferredTaxAssetsNet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:to="us-gaap_DeferredTaxAssetsNet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxLiabilitiesAbstract" xlink:label="us-gaap_DeferredTaxLiabilitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ComponentsOfDeferredTaxLiabilitiesAbstract" xlink:to="us-gaap_DeferredTaxLiabilitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredTaxLiabilitiesRetirementBenefits" xlink:label="jhg_DeferredTaxLiabilitiesRetirementBenefits"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DeferredTaxLiabilitiesAbstract" xlink:to="jhg_DeferredTaxLiabilitiesRetirementBenefits" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets" xlink:label="us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DeferredTaxLiabilitiesAbstract" xlink:to="us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxLiabilitiesOther" xlink:label="us-gaap_DeferredTaxLiabilitiesOther"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DeferredTaxLiabilitiesAbstract" xlink:to="us-gaap_DeferredTaxLiabilitiesOther" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilities" xlink:label="us-gaap_DeferredIncomeTaxLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DeferredTaxLiabilitiesAbstract" xlink:to="us-gaap_DeferredIncomeTaxLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxLiabilities" xlink:label="us-gaap_DeferredTaxLiabilities"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ComponentsOfDeferredTaxLiabilitiesAbstract" xlink:to="us-gaap_DeferredTaxLiabilities" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNetAbstract" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNetAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DeferredTaxAssetsLiabilitiesNetAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsNetNoncurrent" xlink:label="us-gaap_DeferredTaxAssetsNetNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DeferredTaxAssetsLiabilitiesNetAbstract" xlink:to="us-gaap_DeferredTaxAssetsNetNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxLiabilitiesNoncurrent" xlink:label="us-gaap_DeferredTaxLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DeferredTaxAssetsLiabilitiesNetAbstract" xlink:to="us-gaap_DeferredTaxLiabilitiesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:label="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IncomeTaxExpenseBenefitOnUndistributedEarningsOfForeignSubsidiaries" xlink:label="jhg_IncomeTaxExpenseBenefitOnUndistributedEarningsOfForeignSubsidiaries"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_IncomeTaxExpenseBenefitOnUndistributedEarningsOfForeignSubsidiaries" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureOtherFinancialStatementCaptionsDetails" xlink:type="extended" xlink:title="41201 - Disclosure - Other Financial Statement Captions (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="us-gaap_CounterpartyNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_CounterpartyNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="us-gaap_RepurchaseAgreementCounterpartyNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_CounterpartyNameAxis" xlink:to="us-gaap_RepurchaseAgreementCounterpartyNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DaiIchiOptionMember" xlink:label="jhg_DaiIchiOptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="jhg_DaiIchiOptionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OtherAssetsCurrentAbstract" xlink:label="jhg_OtherAssetsCurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_OtherAssetsCurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PrepaidExpenseCurrent" xlink:label="us-gaap_PrepaidExpenseCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_OtherAssetsCurrentAbstract" xlink:to="us-gaap_PrepaidExpenseCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredAcquisitionCostCurrent" xlink:label="jhg_DeferredAcquisitionCostCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_OtherAssetsCurrentAbstract" xlink:to="jhg_DeferredAcquisitionCostCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxesReceivable" xlink:label="us-gaap_IncomeTaxesReceivable"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_OtherAssetsCurrentAbstract" xlink:to="us-gaap_IncomeTaxesReceivable" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsMiscellaneousCurrent" xlink:label="us-gaap_OtherAssetsMiscellaneousCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_OtherAssetsCurrentAbstract" xlink:to="us-gaap_OtherAssetsMiscellaneousCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="us-gaap_OtherAssetsCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_OtherAssetsCurrentAbstract" xlink:to="us-gaap_OtherAssetsCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherAssetsNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesAbstract" xlink:label="us-gaap_OtherLiabilitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherLiabilitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccruedSalesCommissionCurrent" xlink:label="us-gaap_AccruedSalesCommissionCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OtherLiabilitiesAbstract" xlink:to="us-gaap_AccruedSalesCommissionCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AccruedRebatesCurrent" xlink:label="jhg_AccruedRebatesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OtherLiabilitiesAbstract" xlink:to="jhg_AccruedRebatesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OtherMiscellaneousAccruedLiabilitiesCurrent" xlink:label="jhg_OtherMiscellaneousAccruedLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OtherLiabilitiesAbstract" xlink:to="jhg_OtherMiscellaneousAccruedLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_OtherLiabilitiesAbstract" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccruedIncomeTaxesCurrent" xlink:label="us-gaap_AccruedIncomeTaxesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedIncomeTaxesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilitiesCurrent" xlink:label="us-gaap_DerivativeLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_DerivativeLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherSundryLiabilitiesCurrent" xlink:label="us-gaap_OtherSundryLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_OtherSundryLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:label="us-gaap_OtherLiabilitiesNoncurrentAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherLiabilitiesNoncurrentAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccruedIncomeTaxesNoncurrent" xlink:label="us-gaap_AccruedIncomeTaxesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:to="us-gaap_AccruedIncomeTaxesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherSundryLiabilitiesNoncurrent" xlink:label="us-gaap_OtherSundryLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:to="us-gaap_OtherSundryLiabilitiesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:label="us-gaap_DeferredRevenueNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:to="us-gaap_DeferredRevenueNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAccruedLiabilitiesNoncurrent" xlink:label="us-gaap_OtherAccruedLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:to="us-gaap_OtherAccruedLiabilitiesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="us-gaap_OtherLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_OtherLiabilitiesNoncurrentAbstract" xlink:to="us-gaap_OtherLiabilitiesNoncurrent" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureOtherFinancialStatementCaptionsLeasesDetails" xlink:type="extended" xlink:title="41202 - Disclosure - Other Financial Statement Captions - Leases (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:label="us-gaap_ScheduleOfOperatingLeasedAssetsTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LeaseArrangementTypeAxis" xlink:label="us-gaap_LeaseArrangementTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:to="us-gaap_LeaseArrangementTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LeaseArrangementTypeDomain" xlink:label="us-gaap_LeaseArrangementTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_LeaseArrangementTypeAxis" xlink:to="us-gaap_LeaseArrangementTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LeaseArrangementTypeDomain" xlink:label="us-gaap_LeaseArrangementTypeDomain_636553283341745535"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_LeaseArrangementTypeAxis" xlink:to="us-gaap_LeaseArrangementTypeDomain_636553283341745535" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LeaseInLancelotPlaceLondonMember" xlink:label="jhg_LeaseInLancelotPlaceLondonMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LeaseArrangementTypeDomain" xlink:to="jhg_LeaseInLancelotPlaceLondonMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LeaseInRexHouseQueenStreetLondonMember" xlink:label="jhg_LeaseInRexHouseQueenStreetLondonMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LeaseArrangementTypeDomain" xlink:to="jhg_LeaseInRexHouseQueenStreetLondonMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasedAssetsLineItems" xlink:label="us-gaap_OperatingLeasedAssetsLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_OperatingLeasedAssetsLineItems" xlink:to="us-gaap_ScheduleOfOperatingLeasedAssetsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LesseeOperatingLeaseNumber" xlink:label="jhg_LesseeOperatingLeaseNumber"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OperatingLeasedAssetsLineItems" xlink:to="jhg_LesseeOperatingLeaseNumber" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract" xlink:label="us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OperatingLeasedAssetsLineItems" xlink:to="us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureNoncontrollingInterestsRedeemableDetails" xlink:type="extended" xlink:title="41301 - Disclosure - Noncontrolling Interests - Redeemable (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable" xlink:label="us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="us-gaap_ConsolidatedEntitiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable" xlink:to="us-gaap_ConsolidatedEntitiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiariesMember" xlink:label="us-gaap_SubsidiariesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_SubsidiariesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IntechFoundersMember" xlink:label="jhg_IntechFoundersMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="jhg_IntechFoundersMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesMember" xlink:label="us-gaap_ConsolidatedEntitiesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_ConsolidatedEntitiesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentSecondaryCategorizationAxis" xlink:label="us-gaap_InvestmentSecondaryCategorizationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable" xlink:to="us-gaap_InvestmentSecondaryCategorizationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:label="us-gaap_InvestmentsBySecondaryCategorizationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentSecondaryCategorizationAxis" xlink:to="us-gaap_InvestmentsBySecondaryCategorizationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeededInvestmentProductsMember" xlink:label="jhg_SeededInvestmentProductsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeededInvestmentProductsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestLineItems" xlink:label="us-gaap_RedeemableNoncontrollingInterestLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_RedeemableNoncontrollingInterestLineItems" xlink:to="us-gaap_RedeemableNoncontrollingInterestByLegalEntityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityFairValue" xlink:label="us-gaap_RedeemableNoncontrollingInterestEquityFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RedeemableNoncontrollingInterestLineItems" xlink:to="us-gaap_RedeemableNoncontrollingInterestEquityFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AmortizationOfShareBasedIncentiveRights" xlink:label="jhg_AmortizationOfShareBasedIncentiveRights"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RedeemableNoncontrollingInterestLineItems" xlink:to="jhg_AmortizationOfShareBasedIncentiveRights" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MovementInMinorityInterestRollForward" xlink:label="us-gaap_MovementInMinorityInterestRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_RedeemableNoncontrollingInterestLineItems" xlink:to="us-gaap_MovementInMinorityInterestRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MinorityInterestPeriodIncreaseDecreaseRelatingToAcquisitionFromMergerOfSeededInvestmentProducts" xlink:label="jhg_MinorityInterestPeriodIncreaseDecreaseRelatingToAcquisitionFromMergerOfSeededInvestmentProducts"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MovementInMinorityInterestRollForward" xlink:to="jhg_MinorityInterestPeriodIncreaseDecreaseRelatingToAcquisitionFromMergerOfSeededInvestmentProducts" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MinorityInterestPeriodIncreaseDecreaseMarketValueOfSeededInvestmentProducts" xlink:label="jhg_MinorityInterestPeriodIncreaseDecreaseMarketValueOfSeededInvestmentProducts"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MovementInMinorityInterestRollForward" xlink:to="jhg_MinorityInterestPeriodIncreaseDecreaseMarketValueOfSeededInvestmentProducts" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MinorityInterestPeriodIncreaseDecreaseOwnershipInterestOfSeededInvestmentProducts" xlink:label="jhg_MinorityInterestPeriodIncreaseDecreaseOwnershipInterestOfSeededInvestmentProducts"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MovementInMinorityInterestRollForward" xlink:to="jhg_MinorityInterestPeriodIncreaseDecreaseOwnershipInterestOfSeededInvestmentProducts" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MinorityInterestPeriodIncreaseDecreaseRelatingToForeignCurrencyTranslationOfSeededInvestmentProducts" xlink:label="jhg_MinorityInterestPeriodIncreaseDecreaseRelatingToForeignCurrencyTranslationOfSeededInvestmentProducts"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MovementInMinorityInterestRollForward" xlink:to="jhg_MinorityInterestPeriodIncreaseDecreaseRelatingToForeignCurrencyTranslationOfSeededInvestmentProducts" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MinorityInterestRemainingOwnershipPercentage" xlink:label="jhg_MinorityInterestRemainingOwnershipPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_RedeemableNoncontrollingInterestLineItems" xlink:to="jhg_MinorityInterestRemainingOwnershipPercentage" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureNoncontrollingInterestsNonredeemableDetails" xlink:type="extended" xlink:title="41302 - Disclosure - Noncontrolling Interests - Nonredeemable (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestTable" xlink:label="us-gaap_MinorityInterestTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentSecondaryCategorizationAxis" xlink:label="us-gaap_InvestmentSecondaryCategorizationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_MinorityInterestTable" xlink:to="us-gaap_InvestmentSecondaryCategorizationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:label="us-gaap_InvestmentsBySecondaryCategorizationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InvestmentSecondaryCategorizationAxis" xlink:to="us-gaap_InvestmentsBySecondaryCategorizationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeededInvestmentProductsMember" xlink:label="jhg_SeededInvestmentProductsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InvestmentsBySecondaryCategorizationDomain" xlink:to="jhg_SeededInvestmentProductsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="us-gaap_ConsolidatedEntitiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_MinorityInterestTable" xlink:to="us-gaap_ConsolidatedEntitiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="us-gaap_ConsolidatedEntitiesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ConsolidatedEntitiesAxis" xlink:to="us-gaap_ConsolidatedEntitiesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiariesMember" xlink:label="us-gaap_SubsidiariesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsolidatedEntitiesDomain" xlink:to="us-gaap_SubsidiariesMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestLineItems" xlink:label="us-gaap_MinorityInterestLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="us-gaap_MinorityInterestTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestAbstract" xlink:label="us-gaap_MinorityInterestAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MinorityInterestLineItems" xlink:to="us-gaap_MinorityInterestAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterest" xlink:label="us-gaap_MinorityInterest"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MinorityInterestAbstract" xlink:to="us-gaap_MinorityInterest" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationDetails" xlink:type="extended" xlink:title="41401 - Disclosure - Long-Term Incentive Compensation - (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredEquityPlanMember" xlink:label="jhg_DeferredEquityPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_DeferredEquityPlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RestrictedSharePlanMember" xlink:label="jhg_RestrictedSharePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_RestrictedSharePlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BuyAsYouEarnSharePlanMember" xlink:label="jhg_BuyAsYouEarnSharePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_BuyAsYouEarnSharePlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MutualFundShareAwardsMember" xlink:label="jhg_MutualFundShareAwardsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="jhg_MutualFundShareAwardsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_TimeBasedMutualFundShareAwardsMember" xlink:label="jhg_TimeBasedMutualFundShareAwardsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_MutualFundShareAwardsMember" xlink:to="jhg_TimeBasedMutualFundShareAwardsMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PerformanceBasedMutualFundShareAwardsMember" xlink:label="jhg_PerformanceBasedMutualFundShareAwardsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_MutualFundShareAwardsMember" xlink:to="jhg_PerformanceBasedMutualFundShareAwardsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PriceVestingUnitsMember" xlink:label="jhg_PriceVestingUnitsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="jhg_PriceVestingUnitsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PriceVestingUnitsGrantedIn2014Member" xlink:label="jhg_PriceVestingUnitsGrantedIn2014Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_PriceVestingUnitsMember" xlink:to="jhg_PriceVestingUnitsGrantedIn2014Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PriceVestingUnitsGrantedIn2015Member" xlink:label="jhg_PriceVestingUnitsGrantedIn2015Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_PriceVestingUnitsMember" xlink:to="jhg_PriceVestingUnitsGrantedIn2015Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PriceVestingUnitsGrantedIn2016Member" xlink:label="jhg_PriceVestingUnitsGrantedIn2016Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_PriceVestingUnitsMember" xlink:to="jhg_PriceVestingUnitsGrantedIn2016Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeniorProfitsInterestsAwardsMember" xlink:label="jhg_SeniorProfitsInterestsAwardsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="jhg_SeniorProfitsInterestsAwardsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockAppreciationRightsSARSMember" xlink:label="us-gaap_StockAppreciationRightsSARSMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_StockAppreciationRightsSARSMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockAppreciationRightsSars2014Member" xlink:label="jhg_StockAppreciationRightsSars2014Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockAppreciationRightsSARSMember" xlink:to="jhg_StockAppreciationRightsSars2014Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockAppreciationRightsSars2015Member" xlink:label="jhg_StockAppreciationRightsSars2015Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StockAppreciationRightsSARSMember" xlink:to="jhg_StockAppreciationRightsSars2015Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockAppreciationRightsSars2016Member" xlink:label="jhg_StockAppreciationRightsSars2016Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StockAppreciationRightsSARSMember" xlink:to="jhg_StockAppreciationRightsSars2016Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProfitsInterestsMember" xlink:label="jhg_ProfitsInterestsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="jhg_ProfitsInterestsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PhantomShareUnitsPSUsMember" xlink:label="us-gaap_PhantomShareUnitsPSUsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_PhantomShareUnitsPSUsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProfitsInterestAndPhantomInterestsMember" xlink:label="jhg_ProfitsInterestAndPhantomInterestsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="jhg_ProfitsInterestAndPhantomInterestsMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_JanusCapitalGroupIncMember" xlink:label="jhg_JanusCapitalGroupIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="jhg_JanusCapitalGroupIncMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PerkinsInvestmentManagementLLCMember" xlink:label="jhg_PerkinsInvestmentManagementLLCMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="dei_EntityDomain" xlink:to="jhg_PerkinsInvestmentManagementLLCMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_IntechInvestmentManagementLlcMember" xlink:label="jhg_IntechInvestmentManagementLlcMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="dei_EntityDomain" xlink:to="jhg_IntechInvestmentManagementLlcMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="us-gaap_TitleOfIndividualAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_TitleOfIndividualAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TitleOfIndividualAxis" xlink:to="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_636553283341795540"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_TitleOfIndividualAxis" xlink:to="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_636553283341795540" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ChiefExecutiveOfficerMember" xlink:label="us-gaap_ChiefExecutiveOfficerMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="us-gaap_ChiefExecutiveOfficerMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MinimumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardDateAxis" xlink:label="us-gaap_AwardDateAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="6" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardDateAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardDateDomain" xlink:label="us-gaap_AwardDateDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardDateAxis" xlink:to="us-gaap_AwardDateDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardDateDomain" xlink:label="us-gaap_AwardDateDomain_636553283341805541"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AwardDateAxis" xlink:to="us-gaap_AwardDateDomain_636553283341805541" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeniorProfitsInterestsAwardsGrantedOnNovember182013Member" xlink:label="jhg_SeniorProfitsInterestsAwardsGrantedOnNovember182013Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AwardDateDomain" xlink:to="jhg_SeniorProfitsInterestsAwardsGrantedOnNovember182013Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="7" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_BalanceSheetLocationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember" xlink:label="us-gaap_OtherNoncurrentAssetsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherNoncurrentAssetsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualRequisiteServicePeriod1" xlink:label="us-gaap_DeferredCompensationArrangementWithIndividualRequisiteServicePeriod1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_DeferredCompensationArrangementWithIndividualRequisiteServicePeriod1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentagePerYear" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentagePerYear"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentagePerYear" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardConsiderationFromEmployees" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardConsiderationFromEmployees"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardConsiderationFromEmployees" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAmountRequiredByUnvestedAwardsForApprovalOfRemunerationCommittee" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAmountRequiredByUnvestedAwardsForApprovalOfRemunerationCommittee"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAmountRequiredByUnvestedAwardsForApprovalOfRemunerationCommittee" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAmountRequiredByVestedAwardsForApprovalOfRemunerationCommittee" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAmountRequiredByVestedAwardsForApprovalOfRemunerationCommittee"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumAmountRequiredByVestedAwardsForApprovalOfRemunerationCommittee" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualMaximumEmployeeSubscription" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualMaximumEmployeeSubscription"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualMaximumEmployeeSubscription" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfMatchingSharesForEveryShare" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfMatchingSharesForEveryShare"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfMatchingSharesForEveryShare" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalPaymentForEachSharePurchased" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalPaymentForEachSharePurchased"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalPaymentForEachSharePurchased" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfMatchingSharesForfeitedPeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfMatchingSharesForfeitedPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfMatchingSharesForfeitedPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PriceVestingUnitsAbstract" xlink:label="jhg_PriceVestingUnitsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_PriceVestingUnitsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_PriceVestingUnitsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsValueOfGrantsInPeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsValueOfGrantsInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_PriceVestingUnitsAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsValueOfGrantsInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_PriceVestingUnitsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MutualFundShareAwardsAbstract" xlink:label="jhg_MutualFundShareAwardsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_MutualFundShareAwardsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SeniorProfitsInterestsAbstract" xlink:label="jhg_SeniorProfitsInterestsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_SeniorProfitsInterestsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent" xlink:label="us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_SeniorProfitsInterestsAbstract" xlink:to="us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PercentageOfAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitled" xlink:label="jhg_PercentageOfAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitled"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_SeniorProfitsInterestsAbstract" xlink:to="jhg_PercentageOfAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitled" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PercentageOfAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitledInYearTwo" xlink:label="jhg_PercentageOfAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitledInYearTwo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_SeniorProfitsInterestsAbstract" xlink:to="jhg_PercentageOfAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitledInYearTwo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PercentageOfIncreaseInAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitledAfterYearTwo" xlink:label="jhg_PercentageOfIncreaseInAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitledAfterYearTwo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_SeniorProfitsInterestsAbstract" xlink:to="jhg_PercentageOfIncreaseInAnnualTaxableIncomeToWhichSeniorProfitInterestAwardsAreEntitledAfterYearTwo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFormulaDrivenValue" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFormulaDrivenValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_SeniorProfitsInterestsAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFormulaDrivenValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LongTermIncentiveAwardsAbstract" xlink:label="jhg_LongTermIncentiveAwardsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_LongTermIncentiveAwardsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EmployeeServiceShareBasedCompensationFairValueAtAcquisitionDate" xlink:label="jhg_EmployeeServiceShareBasedCompensationFairValueAtAcquisitionDate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="jhg_EmployeeServiceShareBasedCompensationFairValueAtAcquisitionDate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PercentageOfEquityLikeStakeInPreIncentiveProfits" xlink:label="jhg_PercentageOfEquityLikeStakeInPreIncentiveProfits"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="jhg_PercentageOfEquityLikeStakeInPreIncentiveProfits" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MaximumPeriodForWhichDistributionAreMadeUnderProfitsInterestsPostEmployment" xlink:label="jhg_MaximumPeriodForWhichDistributionAreMadeUnderProfitsInterestsPostEmployment"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="jhg_MaximumPeriodForWhichDistributionAreMadeUnderProfitsInterestsPostEmployment" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsDiscountRate" xlink:label="us-gaap_FairValueInputsDiscountRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="us-gaap_FairValueInputsDiscountRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_UndiscountedEstimatedPostEmploymentPayments" xlink:label="jhg_UndiscountedEstimatedPostEmploymentPayments"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="jhg_UndiscountedEstimatedPostEmploymentPayments" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProfitsInterestAndPhantomInterestsInSubsidiary" xlink:label="jhg_ProfitsInterestAndPhantomInterestsInSubsidiary"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="jhg_ProfitsInterestAndPhantomInterestsInSubsidiary" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SharebasedCompensationArrangementPeriodOfTimeRightsOrSharesAreExercised" xlink:label="jhg_SharebasedCompensationArrangementPeriodOfTimeRightsOrSharesAreExercised"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="jhg_LongTermIncentiveAwardsAbstract" xlink:to="jhg_SharebasedCompensationArrangementPeriodOfTimeRightsOrSharesAreExercised" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LongTermIncentiveStockPlansAbstract" xlink:label="jhg_LongTermIncentiveStockPlansAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="jhg_LongTermIncentiveStockPlansAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_LongTermIncentiveStockPlansAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationCompensationPlansDetails" xlink:type="extended" xlink:title="41402 - Disclosure - Long-Term Incentive Compensation - Compensation Plans (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_EmployeeShareOwnershipPlanMember" xlink:label="jhg_EmployeeShareOwnershipPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_EmployeeShareOwnershipPlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredEquityPlanMember" xlink:label="jhg_DeferredEquityPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_DeferredEquityPlanMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RestrictedSharePlanMember" xlink:label="jhg_RestrictedSharePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_RestrictedSharePlanMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_BuyAsYouEarnSharePlanMember" xlink:label="jhg_BuyAsYouEarnSharePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_BuyAsYouEarnSharePlanMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SharesavePlanMember" xlink:label="jhg_SharesavePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_SharesavePlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_UsSharesavePlanMember" xlink:label="jhg_UsSharesavePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_SharesavePlanMember" xlink:to="jhg_UsSharesavePlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RestrictedStockAwardMember" xlink:label="jhg_RestrictedStockAwardMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_RestrictedStockAwardMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_CompanyShareOptionPlanMember" xlink:label="jhg_CompanyShareOptionPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_CompanyShareOptionPlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_UsCompanyShareOptionPlanMember" xlink:label="jhg_UsCompanyShareOptionPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_CompanyShareOptionPlanMember" xlink:to="jhg_UsCompanyShareOptionPlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ExecutiveSharedOwnershipPlanMember" xlink:label="jhg_ExecutiveSharedOwnershipPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_ExecutiveSharedOwnershipPlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ExecutiveSharedOwnership2017PlanMember" xlink:label="jhg_ExecutiveSharedOwnership2017PlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_ExecutiveSharedOwnershipPlanMember" xlink:to="jhg_ExecutiveSharedOwnership2017PlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ExecutiveSharedOwnership2014PlanMember" xlink:label="jhg_ExecutiveSharedOwnership2014PlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_ExecutiveSharedOwnershipPlanMember" xlink:to="jhg_ExecutiveSharedOwnership2014PlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LongtermIncentivePlanMember" xlink:label="jhg_LongtermIncentivePlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_LongtermIncentivePlanMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_Ltip2013Member" xlink:label="jhg_Ltip2013Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_LongtermIncentivePlanMember" xlink:to="jhg_Ltip2013Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_Ltip2014Member" xlink:label="jhg_Ltip2014Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_LongtermIncentivePlanMember" xlink:to="jhg_Ltip2014Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_Ltip2015Member" xlink:label="jhg_Ltip2015Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_LongtermIncentivePlanMember" xlink:to="jhg_Ltip2015Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_Ltip2016Member" xlink:label="jhg_Ltip2016Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_LongtermIncentivePlanMember" xlink:to="jhg_Ltip2016Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="us-gaap_TitleOfIndividualAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_TitleOfIndividualAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_TitleOfIndividualAxis" xlink:to="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_UkEmployeesMember" xlink:label="jhg_UkEmployeesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="jhg_UkEmployeesMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VestingCriteriaAxis" xlink:label="jhg_VestingCriteriaAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="jhg_VestingCriteriaAxis" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VestingCriteriaDomain" xlink:label="jhg_VestingCriteriaDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="jhg_VestingCriteriaAxis" xlink:to="jhg_VestingCriteriaDomain" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_VestingCriteriaDomain" xlink:label="jhg_VestingCriteriaDomain_636553283341925553"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="jhg_VestingCriteriaAxis" xlink:to="jhg_VestingCriteriaDomain_636553283341925553" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RelativeTotalShareholderReturnMember" xlink:label="jhg_RelativeTotalShareholderReturnMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_RelativeTotalShareholderReturnMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RelativeInvestmentPerformanceMember" xlink:label="jhg_RelativeInvestmentPerformanceMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_RelativeInvestmentPerformanceMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RelativeNetIncomeBeforeTaxGrowthMember" xlink:label="jhg_RelativeNetIncomeBeforeTaxGrowthMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_RelativeNetIncomeBeforeTaxGrowthMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_Ftse350Member" xlink:label="jhg_Ftse350Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_Ftse350Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_Asx100Member" xlink:label="jhg_Asx100Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_Asx100Member" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_NetFundFlowsConditionMember" xlink:label="jhg_NetFundFlowsConditionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_NetFundFlowsConditionMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_InvestmentPerformanceConditionMember" xlink:label="jhg_InvestmentPerformanceConditionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_InvestmentPerformanceConditionMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OperatingMarginConditionMember" xlink:label="jhg_OperatingMarginConditionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_OperatingMarginConditionMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PeopleStrategyConditionMember" xlink:label="jhg_PeopleStrategyConditionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="jhg_VestingCriteriaDomain" xlink:to="jhg_PeopleStrategyConditionMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingAxis" xlink:label="us-gaap_VestingAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_VestingAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingDomain" xlink:label="us-gaap_VestingDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VestingAxis" xlink:to="us-gaap_VestingDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingDomain" xlink:label="us-gaap_VestingDomain_636553283341935554"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_VestingAxis" xlink:to="us-gaap_VestingDomain_636553283341935554" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_VestingDomain" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheOneMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_VestingDomain" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheTwoMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMonthlyMaximumEmployeeSubscription" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMonthlyMaximumEmployeeSubscription"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardMonthlyMaximumEmployeeSubscription" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionExercisablePeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionExercisablePeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionExercisablePeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardHurdlePrice" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardHurdlePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardHurdlePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceHurdleRelatedToGroupTsrPercentage" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceHurdleRelatedToGroupTsrPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceHurdleRelatedToGroupTsrPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceHurdleRelatedToRiskAndSustainabilityMetrics" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceHurdleRelatedToRiskAndSustainabilityMetrics"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerformanceHurdleRelatedToRiskAndSustainabilityMetrics" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePercentageFromEndOfYearThree" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePercentageFromEndOfYearThree"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePercentageFromEndOfYearThree" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePercentageFromEndOfYearFour" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePercentageFromEndOfYearFour"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePercentageFromEndOfYearFour" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingCriteriaWeightagePercentage" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingCriteriaWeightagePercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingCriteriaWeightagePercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalHoldingPeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalHoldingPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalHoldingPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardsToBeVestedRightsPercentage" xlink:label="jhg_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardsToBeVestedRightsPercentage"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardsToBeVestedRightsPercentage" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsToBeVestedRightsPercentagePreMerger" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsToBeVestedRightsPercentagePreMerger"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsToBeVestedRightsPercentagePreMerger" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsToBeVestedRightsPercentagePostMerger" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsToBeVestedRightsPercentagePostMerger"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardsToBeVestedRightsPercentagePostMerger" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LiabilitySettledOfShareBasedAwardPlan" xlink:label="jhg_LiabilitySettledOfShareBasedAwardPlan"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="21" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_LiabilitySettledOfShareBasedAwardPlan" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MutualFundShareAwardsLiabilitySettledOfShareBasedAwardPlan" xlink:label="jhg_MutualFundShareAwardsLiabilitySettledOfShareBasedAwardPlan"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="22" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_MutualFundShareAwardsLiabilitySettledOfShareBasedAwardPlan" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProfitsInterestsAndOtherShareBasedAwardPlan" xlink:label="jhg_ProfitsInterestsAndOtherShareBasedAwardPlan"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="23" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ProfitsInterestsAndOtherShareBasedAwardPlan" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SocialSecurityCostsShareBasedAwardPlan" xlink:label="jhg_SocialSecurityCostsShareBasedAwardPlan"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="24" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_SocialSecurityCostsShareBasedAwardPlan" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_StockBasedPaymentExpenseChargedToComprehensiveIncome" xlink:label="jhg_StockBasedPaymentExpenseChargedToComprehensiveIncome"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="25" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_StockBasedPaymentExpenseChargedToComprehensiveIncome" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="26" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="27" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlan" xlink:label="jhg_LiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlan"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="28" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_LiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlan" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MutualFundShareAwardsLiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlan" xlink:label="jhg_MutualFundShareAwardsLiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlan"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="29" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_MutualFundShareAwardsLiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlan" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProfitsInterestsAndOtherShareBasedAwardPlanUnrecognisedCompensation" xlink:label="jhg_ProfitsInterestsAndOtherShareBasedAwardPlanUnrecognisedCompensation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="30" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ProfitsInterestsAndOtherShareBasedAwardPlanUnrecognisedCompensation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SocialSecurityCostsShareBasedAwardPlanUnrecognisedCompensation" xlink:label="jhg_SocialSecurityCostsShareBasedAwardPlanUnrecognisedCompensation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="31" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_SocialSecurityCostsShareBasedAwardPlanUnrecognisedCompensation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_UnrecognisedCompensationCostsChargedToComprehensiveIncomeRemaining" xlink:label="jhg_UnrecognisedCompensationCostsChargedToComprehensiveIncomeRemaining"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="32" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_UnrecognisedCompensationCostsChargedToComprehensiveIncomeRemaining" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlanWeightedAverageYears" xlink:label="jhg_LiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlanWeightedAverageYears"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="33" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_LiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlanWeightedAverageYears" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MutualFundShareAwardsLiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlanWeightedAverageYears" xlink:label="jhg_MutualFundShareAwardsLiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlanWeightedAverageYears"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="34" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_MutualFundShareAwardsLiabilitySettledOfUnrecognisedCompensationShareBasedAwardPlanWeightedAverageYears" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ProfitsInterestsAndOtherWeightedAverageYears" xlink:label="jhg_ProfitsInterestsAndOtherWeightedAverageYears"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="35" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ProfitsInterestsAndOtherWeightedAverageYears" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_SocialSecurityCostsWeightedAverageYears" xlink:label="jhg_SocialSecurityCostsWeightedAverageYears"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="36" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_SocialSecurityCostsWeightedAverageYears" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_UnrecognisedCompensationWeightedAverageYearsChargeToComprehensiveIncomeRemaining" xlink:label="jhg_UnrecognisedCompensationWeightedAverageYearsChargeToComprehensiveIncomeRemaining"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="37" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_UnrecognisedCompensationWeightedAverageYearsChargeToComprehensiveIncomeRemaining" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="38" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="39" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_PercentageOfAllocationOfAwardFairValues" xlink:label="jhg_PercentageOfAllocationOfAwardFairValues"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:to="jhg_PercentageOfAllocationOfAwardFairValues" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValueMonteCarlo" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValueMonteCarlo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValueMonteCarlo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMonteCarlo" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMonteCarlo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMonteCarlo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRateMonteCarlo" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRateMonteCarlo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRateMonteCarlo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMonteCarlo" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMonteCarlo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMonteCarlo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsHoldingPeriodAdjustmentPercentageMonteCarlo" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsHoldingPeriodAdjustmentPercentageMonteCarlo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsHoldingPeriodAdjustmentPercentageMonteCarlo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsPercentageBasedOnPreModificationMonteCarlo" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsPercentageBasedOnPreModificationMonteCarlo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyMonteCarloAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsPercentageBasedOnPreModificationMonteCarlo" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureLongTermIncentiveCompensationEsopAndRsaDetails" xlink:type="extended" xlink:title="41403 - Disclosure - Long-Term Incentive Compensation - ESOP and RSA (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DeferredEquityPlanMember" xlink:label="jhg_DeferredEquityPlanMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="jhg_DeferredEquityPlanMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsShareConsolidatedInPeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsShareConsolidatedInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsShareConsolidatedInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsShareAcquiredFromMergerInPeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsShareAcquiredFromMergerInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsShareAcquiredFromMergerInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsSharesConsolidatedInPeriodWeightedAverageConsolidationPrice" xlink:label="jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsSharesConsolidatedInPeriodWeightedAverageConsolidationPrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsSharesConsolidatedInPeriodWeightedAverageConsolidationPrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsSharesAcquiredInPeriodWeightedAverageAcquisitionPrice" xlink:label="jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsSharesAcquiredInPeriodWeightedAverageAcquisitionPrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsSharesAcquiredInPeriodWeightedAverageAcquisitionPrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueOfOptionsAbstract" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueOfOptionsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueOfOptionsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueOfOptionsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueOfOptionsAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardIntrinsicValueOfOptionsAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareAcquiredFromMergerInPeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareAcquiredFromMergerInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareAcquiredFromMergerInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareConsolidation" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareConsolidation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareConsolidation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPeriodIncreaseDecrease" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPeriodIncreaseDecrease"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPeriodIncreaseDecrease" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareConsolidatedInPeriodWeightedAverageGrantDateFairValue" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareConsolidatedInPeriodWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareConsolidatedInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharesAcquiredInPeriodWeightedAverageAcquisitionPrice" xlink:label="jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharesAcquiredInPeriodWeightedAverageAcquisitionPrice"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:to="jhg_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharesAcquiredInPeriodWeightedAverageAcquisitionPrice" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustmentsInPeriodWeightedAverageGrantDateFairValue" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustmentsInPeriodWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdjustmentsInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriodWeightedAverageGrantDateFairValue" xlink:label="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriodWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:to="jhg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureRetirementBenefitPlansDetails" xlink:type="extended" xlink:title="41501 - Disclosure - Retirement benefit plans (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable" xlink:label="us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable" xlink:to="us-gaap_RangeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_MaximumMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="us-gaap_StatementGeographicalAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable" xlink:to="us-gaap_StatementGeographicalAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="us-gaap_SegmentGeographicalDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementGeographicalAxis" xlink:to="us-gaap_SegmentGeographicalDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_US" xlink:label="country_US"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="country_US" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonUsMember" xlink:label="us-gaap_NonUsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="us-gaap_NonUsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="us-gaap_RetirementPlanTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable" xlink:to="us-gaap_RetirementPlanTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="us-gaap_RetirementPlanTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RetirementPlanTypeAxis" xlink:to="us-gaap_RetirementPlanTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="us-gaap_RetirementPlanTypeDomain_636553283342105571"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_RetirementPlanTypeAxis" xlink:to="us-gaap_RetirementPlanTypeDomain_636553283342105571" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="us-gaap_PensionPlansDefinedBenefitMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RetirementPlanTypeDomain" xlink:to="us-gaap_PensionPlansDefinedBenefitMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent" xlink:label="us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedContributionPlanCostRecognized" xlink:label="us-gaap_DefinedContributionPlanCostRecognized"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="us-gaap_DefinedContributionPlanCostRecognized" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract" xlink:label="us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedContributionPlanContributionAmount" xlink:label="jhg_DefinedContributionPlanContributionAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract" xlink:to="jhg_DefinedContributionPlanContributionAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPensionPlansAndDefinedBenefitPostretirementPlansDisclosureAbstract" xlink:label="us-gaap_DefinedBenefitPensionPlansAndDefinedBenefitPostretirementPlansDisclosureAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="us-gaap_DefinedBenefitPensionPlansAndDefinedBenefitPostretirementPlansDisclosureAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanDeficitOnTriennialValuationOfHGPS" xlink:label="jhg_DefinedBenefitPlanDeficitOnTriennialValuationOfHGPS"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPensionPlansAndDefinedBenefitPostretirementPlansDisclosureAbstract" xlink:to="jhg_DefinedBenefitPlanDeficitOnTriennialValuationOfHGPS" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanContributionsPerAnnum" xlink:label="jhg_DefinedBenefitPlanContributionsPerAnnum"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPensionPlansAndDefinedBenefitPostretirementPlansDisclosureAbstract" xlink:to="jhg_DefinedBenefitPlanContributionsPerAnnum" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanNumberOfYearsOfContribution" xlink:label="jhg_DefinedBenefitPlanNumberOfYearsOfContribution"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPensionPlansAndDefinedBenefitPostretirementPlansDisclosureAbstract" xlink:to="jhg_DefinedBenefitPlanNumberOfYearsOfContribution" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureRetirementBenefitPlansChangeInPlanAssetsAndBenefitObligationsNetRetirementBenefitRecognizedInBalanceSheetAssumptionsDetails" xlink:type="extended" xlink:title="41502 - Disclosure - Retirement benefit plans - Change in plan assets and benefit obligations, net retirement benefit recognized in balance sheet, assumptions (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="us-gaap_RetirementPlanTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_RetirementPlanTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="us-gaap_RetirementPlanTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RetirementPlanTypeAxis" xlink:to="us-gaap_RetirementPlanTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="us-gaap_PensionPlansDefinedBenefitMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RetirementPlanTypeDomain" xlink:to="us-gaap_PensionPlansDefinedBenefitMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" xlink:label="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets" xlink:label="us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" xlink:to="us-gaap_DefinedBenefitPlanFairValueOfPlanAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets" xlink:label="us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" xlink:to="us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer" xlink:label="us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" xlink:to="us-gaap_DefinedBenefitPlanContributionsByEmployer" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid" xlink:label="us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" xlink:to="us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanSettlementsPlanAssets" xlink:label="us-gaap_DefinedBenefitPlanSettlementsPlanAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" xlink:to="us-gaap_DefinedBenefitPlanSettlementsPlanAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanPlanAssetsForeignCurrencyTranslationGainLoss" xlink:label="us-gaap_DefinedBenefitPlanPlanAssetsForeignCurrencyTranslationGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward" xlink:to="us-gaap_DefinedBenefitPlanPlanAssetsForeignCurrencyTranslationGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:label="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanBenefitObligation" xlink:label="us-gaap_DefinedBenefitPlanBenefitObligation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="us-gaap_DefinedBenefitPlanBenefitObligation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost" xlink:label="us-gaap_DefinedBenefitPlanServiceCost"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="us-gaap_DefinedBenefitPlanServiceCost" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost" xlink:label="us-gaap_DefinedBenefitPlanInterestCost"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="us-gaap_DefinedBenefitPlanInterestCost" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement" xlink:label="us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="us-gaap_DefinedBenefitPlanBenefitObligationPaymentForSettlement" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid" xlink:label="us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanActuarialGainLoss" xlink:label="us-gaap_DefinedBenefitPlanActuarialGainLoss"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="us-gaap_DefinedBenefitPlanActuarialGainLoss" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation" xlink:label="us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan" xlink:label="us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanFundedStatusOfPlan" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanTax" xlink:label="jhg_DefinedBenefitPlanTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_DefinedBenefitPlanTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet" xlink:label="us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheetAbstract" xlink:label="us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheetAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheetAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_AssetDefinedBenefitPlanAbstract" xlink:label="jhg_AssetDefinedBenefitPlanAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheetAbstract" xlink:to="jhg_AssetDefinedBenefitPlanAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent" xlink:label="us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_AssetDefinedBenefitPlanAbstract" xlink:to="us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansNoncurrentLiabilitiesAbstract" xlink:label="us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansNoncurrentLiabilitiesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheetAbstract" xlink:to="us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansNoncurrentLiabilitiesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent" xlink:label="us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansNoncurrentLiabilitiesAbstract" xlink:to="us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:label="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" xlink:label="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationSalariesInflation" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationSalariesInflation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationSalariesInflation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRetailPriceIndexInflation" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRetailPriceIndexInflation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRetailPriceIndexInflation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationConsumerPriceIndexInflation" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationConsumerPriceIndexInflation"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationConsumerPriceIndexInflation" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationPensionIncreaseRpiCappedAt5P.a" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationPensionIncreaseRpiCappedAt5P.a"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationPensionIncreaseRpiCappedAt5P.a" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationPensionIncreaseRpiCappedAt2.5P.a" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationPensionIncreaseRpiCappedAt2.5P.a"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationPensionIncreaseRpiCappedAt2.5P.a" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationLifeExpectancyOfMaleAged60AtAccountingDate" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationLifeExpectancyOfMaleAged60AtAccountingDate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationLifeExpectancyOfMaleAged60AtAccountingDate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationLifeExpectancyOfMaleAged60At15YearsInTime" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationLifeExpectancyOfMaleAged60At15YearsInTime"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationLifeExpectancyOfMaleAged60At15YearsInTime" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationNumberOfYearsInTime" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationNumberOfYearsInTime"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingBenefitObligationAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationNumberOfYearsInTime" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureRetirementBenefitPlansPlanAssetsDetails" xlink:type="extended" xlink:title="41503 - Disclosure - Retirement benefit plans - Plan assets (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="us-gaap_RetirementPlanTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="us-gaap_RetirementPlanTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="us-gaap_RetirementPlanTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RetirementPlanTypeAxis" xlink:to="us-gaap_RetirementPlanTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="us-gaap_PensionPlansDefinedBenefitMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RetirementPlanTypeDomain" xlink:to="us-gaap_PensionPlansDefinedBenefitMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:label="us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="us-gaap_PlanAssetCategoriesDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="us-gaap_PlanAssetCategoriesDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="us-gaap_PlanAssetCategoriesDomain_636553283342175578"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="us-gaap_PlanAssetCategoriesDomain_636553283342175578" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsMember" xlink:label="us-gaap_CashAndCashEquivalentsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanAssetCategoriesDomain" xlink:to="us-gaap_CashAndCashEquivalentsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_MoneyMarketInstrumentsMember" xlink:label="jhg_MoneyMarketInstrumentsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PlanAssetCategoriesDomain" xlink:to="jhg_MoneyMarketInstrumentsMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ForeignExchangeContractMember" xlink:label="us-gaap_ForeignExchangeContractMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PlanAssetCategoriesDomain" xlink:to="us-gaap_ForeignExchangeContractMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BondOptionMember" xlink:label="us-gaap_BondOptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_PlanAssetCategoriesDomain" xlink:to="us-gaap_BondOptionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityFundsMember" xlink:label="us-gaap_EquityFundsMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_PlanAssetCategoriesDomain" xlink:to="us-gaap_EquityFundsMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_GrowthPortfolioMember" xlink:label="jhg_GrowthPortfolioMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_PlanAssetCategoriesDomain" xlink:to="jhg_GrowthPortfolioMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanFairValueOfPlanAssetsAbstract" xlink:label="jhg_DefinedBenefitPlanFairValueOfPlanAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="jhg_DefinedBenefitPlanFairValueOfPlanAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets" xlink:label="us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_DefinedBenefitPlanFairValueOfPlanAssetsAbstract" xlink:to="us-gaap_DefinedBenefitPlanFairValueOfPlanAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanFairValueOfPlanAssetsHeldInManagedFunds" xlink:label="jhg_DefinedBenefitPlanFairValueOfPlanAssetsHeldInManagedFunds"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_DefinedBenefitPlanFairValueOfPlanAssetsAbstract" xlink:to="jhg_DefinedBenefitPlanFairValueOfPlanAssetsHeldInManagedFunds" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations" xlink:label="us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_DefinedBenefitPlanFairValueOfPlanAssetsAbstract" xlink:to="us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward" xlink:label="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets" xlink:label="us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward" xlink:to="us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements" xlink:label="us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward" xlink:to="us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ExpectedRateOfReturnOnPlanAssets" xlink:label="jhg_ExpectedRateOfReturnOnPlanAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward" xlink:to="jhg_ExpectedRateOfReturnOnPlanAssets" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureRetirementBenefitPlansActuarialGainsLossesBenefitCostCashFlowsDetails" xlink:type="extended" xlink:title="41504 - Disclosure - Retirement benefit plans - Actuarial gains(losses), benefit cost, cash flows (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="us-gaap_RetirementPlanTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_RetirementPlanTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="us-gaap_RetirementPlanTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RetirementPlanTypeAxis" xlink:to="us-gaap_RetirementPlanTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="us-gaap_PensionPlansDefinedBenefitMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RetirementPlanTypeDomain" xlink:to="us-gaap_PensionPlansDefinedBenefitMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" xlink:label="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainBeginningBalance" xlink:label="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainBeginningBalance"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" xlink:to="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainBeginningBalance" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainBeforeTax" xlink:label="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainBeforeTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" xlink:to="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainBeforeTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainTax" xlink:label="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" xlink:to="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainSettlementEventBeforeTax" xlink:label="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainSettlementEventBeforeTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" xlink:to="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainSettlementEventBeforeTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainLossSettelementEventTax" xlink:label="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainLossSettelementEventTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" xlink:to="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainLossSettelementEventTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainEndingBalance" xlink:label="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainEndingBalance"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="jhg_DefinedBenefitPlanActuarialGainsAndLossesAbstract" xlink:to="jhg_DefinedBenefitPlanAccumulatedUnamortizedActuarialGainEndingBalance" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear" xlink:label="us-gaap_DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:label="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost" xlink:label="us-gaap_DefinedBenefitPlanServiceCost"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:to="us-gaap_DefinedBenefitPlanServiceCost" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1" xlink:label="us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:to="us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost" xlink:label="us-gaap_DefinedBenefitPlanInterestCost"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:to="us-gaap_DefinedBenefitPlanInterestCost" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets" xlink:label="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:to="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanPeriodicBenefitCostCreditBeforeContributionToMoneyPurchaseSection" xlink:label="jhg_DefinedBenefitPlanPeriodicBenefitCostCreditBeforeContributionToMoneyPurchaseSection"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanPeriodicBenefitCostCreditBeforeContributionToMoneyPurchaseSection" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanContributionToMoneyPurchaseSection" xlink:label="jhg_DefinedBenefitPlanContributionToMoneyPurchaseSection"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanContributionToMoneyPurchaseSection" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" xlink:label="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:to="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:label="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate" xlink:label="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostInflationSalaries" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostInflationSalaries"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostInflationSalaries" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostInflationRetailPriceIndex" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostInflationRetailPriceIndex"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostInflationRetailPriceIndex" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostConsumerPriceIndex" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostConsumerPriceIndex"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostConsumerPriceIndex" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostPensionIncreaseRpiCappedAt5P.a" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostPensionIncreaseRpiCappedAt5P.a"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostPensionIncreaseRpiCappedAt5P.a" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostPensionIncreaseRpiCappedAt2.5P.a" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostPensionIncreaseRpiCappedAt2.5P.a"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostPensionIncreaseRpiCappedAt2.5P.a" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets" xlink:label="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostAmortizationPeriodForNetActuarialGainsLosses" xlink:label="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostAmortizationPeriodForNetActuarialGainsLosses"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract" xlink:to="jhg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostAmortizationPeriodForNetActuarialGainsLosses" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DefinedBenefitPlanPlanAssetsContributionsByEmployerExcludingCreditsToMemberSMoneyPurchaseAccounts" xlink:label="jhg_DefinedBenefitPlanPlanAssetsContributionsByEmployerExcludingCreditsToMemberSMoneyPurchaseAccounts"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_DefinedBenefitPlanPlanAssetsContributionsByEmployerExcludingCreditsToMemberSMoneyPurchaseAccounts" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear" xlink:label="us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" xlink:label="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths" xlink:label="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" xlink:to="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo" xlink:label="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" xlink:to="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree" xlink:label="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" xlink:to="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour" xlink:label="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" xlink:to="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive" xlink:label="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" xlink:to="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter" xlink:label="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract" xlink:to="us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureAccumulatedOtherComprehensiveLossDetails" xlink:type="extended" xlink:title="41601 - Disclosure - Accumulated Other Comprehensive Loss (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember" xlink:label="us-gaap_AccumulatedTranslationAdjustmentMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:to="us-gaap_AccumulatedTranslationAdjustmentMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:label="us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:to="us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:to="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward" xlink:label="us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="us-gaap_AOCIAttributableToParentNetOfTaxRollForward" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AOCIAttributableToParentNetOfTaxRollForward" xlink:to="us-gaap_StockholdersEquity" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent" xlink:label="us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AOCIAttributableToParentNetOfTaxRollForward" xlink:to="us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AOCIAttributableToParentNetOfTaxRollForward" xlink:to="us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AOCIAttributableToParentNetOfTaxRollForward" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AOCIAttributableToParentNetOfTaxRollForward" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureAccumulatedOtherComprehensiveLossOciDetails" xlink:type="extended" xlink:title="41602 - Disclosure - Accumulated Other Comprehensive Loss - OCI (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:label="us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember" xlink:label="us-gaap_AccumulatedTranslationAdjustmentMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedTranslationAdjustmentMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ReclassificationForItemsIncludedInNetIncomeMember" xlink:label="jhg_ReclassificationForItemsIncludedInNetIncomeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EquityComponentDomain" xlink:to="jhg_ReclassificationForItemsIncludedInNetIncomeMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OtherComprehensiveIncomeLossAbstract" xlink:label="jhg_OtherComprehensiveIncomeLossAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="jhg_OtherComprehensiveIncomeLossAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_OtherComprehensiveIncomeLossAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1" xlink:label="us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="jhg_OtherComprehensiveIncomeLossAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="jhg_OtherComprehensiveIncomeLossAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTax" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureEarningsAndDividendsPerShareDetails" xlink:type="extended" xlink:title="41701 - Disclosure - Earnings and Dividends Per Share (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_636553283342245585"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain_636553283342245585" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_RestrictedStockAndUnvestedNonparticipatingStockAwardMember" xlink:label="jhg_RestrictedStockAndUnvestedNonparticipatingStockAwardMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="jhg_RestrictedStockAndUnvestedNonparticipatingStockAwardMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DaiIchiOptionMember" xlink:label="jhg_DaiIchiOptionMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="jhg_DaiIchiOptionMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:label="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UndistributedEarnings" xlink:label="us-gaap_UndistributedEarnings"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:to="us-gaap_UndistributedEarnings" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic" xlink:label="us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:to="us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:to="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:to="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareBasicAbstract" xlink:label="us-gaap_EarningsPerShareBasicAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_EarningsPerShareBasicOtherDisclosuresAbstract" xlink:to="us-gaap_EarningsPerShareBasicAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EarningsPerShareBasicAbstract" xlink:to="us-gaap_EarningsPerShareBasic" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EarningsPerShareBasicAbstract" xlink:to="us-gaap_EarningsPerShareDiluted" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_CommonStockDividendsPerShareCashPaidPreMerger" xlink:label="jhg_CommonStockDividendsPerShareCashPaidPreMerger"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="jhg_CommonStockDividendsPerShareCashPaidPreMerger" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_CommonStockDividendsPerShareCashPaidPostMerger" xlink:label="jhg_CommonStockDividendsPerShareCashPaidPostMerger"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="jhg_CommonStockDividendsPerShareCashPaidPostMerger" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureRelatedPartyTransactionsDetails" xlink:type="extended" xlink:title="41901 - Disclosure - Related Party Transactions (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="dei_LegalEntityAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DaiichiLifeHoldingsIncMember" xlink:label="jhg_DaiichiLifeHoldingsIncMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="dei_EntityDomain" xlink:to="jhg_DaiichiLifeHoldingsIncMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="us-gaap_RelatedPartyTransactionLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueFromRelatedParties" xlink:label="us-gaap_RevenueFromRelatedParties"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_RevenueFromRelatedParties" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DistributionAndServicingFees" xlink:label="us-gaap_DistributionAndServicingFees"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_DistributionAndServicingFees" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DueFromRelatedPartiesCurrent" xlink:label="us-gaap_DueFromRelatedPartiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_DueFromRelatedPartiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableRelatedPartiesCurrent" xlink:label="us-gaap_AccountsReceivableRelatedPartiesCurrent"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="us-gaap_AccountsReceivableRelatedPartiesCurrent" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_InvestmentManagementPerformanceAndShareOwnerServicingFees" xlink:label="jhg_InvestmentManagementPerformanceAndShareOwnerServicingFees"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_RelatedPartyTransactionLineItems" xlink:to="jhg_InvestmentManagementPerformanceAndShareOwnerServicingFees" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureGeographicInformationDetails" xlink:type="extended" xlink:title="42001 - Disclosure - Geographic Information (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:label="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="us-gaap_StatementGeographicalAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:to="us-gaap_StatementGeographicalAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="us-gaap_SegmentGeographicalDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementGeographicalAxis" xlink:to="us-gaap_SegmentGeographicalDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_GB" xlink:label="country_GB"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="country_GB" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LuxembourgMember" xlink:label="jhg_LuxembourgMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="jhg_LuxembourgMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_US" xlink:label="country_US"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="country_US" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_AU" xlink:label="country_AU"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="country_AU" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_InternationalMember" xlink:label="jhg_InternationalMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="jhg_InternationalMember" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_OtherCountryExceptUnitedKingdomAndUnitedStatesMember" xlink:label="jhg_OtherCountryExceptUnitedKingdomAndUnitedStatesMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SegmentGeographicalDomain" xlink:to="jhg_OtherCountryExceptUnitedKingdomAndUnitedStatesMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:label="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:to="us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="us-gaap_RevenuesAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:to="us-gaap_RevenuesAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RevenuesAbstract" xlink:to="us-gaap_Revenues" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_LongLivedAssetsAbstract" xlink:label="jhg_LongLivedAssetsAbstract"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:to="jhg_LongLivedAssetsAbstract" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncurrentAssets" xlink:label="us-gaap_NoncurrentAssets"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="jhg_LongLivedAssetsAbstract" xlink:to="us-gaap_NoncurrentAssets" priority="1" use="optional"/>
</definitionLink>
<definitionLink xlink:role="http://www.janus.com/role/DisclosureSubsequentEventsDetails" xlink:type="extended" xlink:title="42201 - Disclosure - Subsequent Events (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTable" xlink:label="us-gaap_SubsequentEventTable"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_SubsequentEventTypeAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain_636553283342325593"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" order="1" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain_636553283342325593" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_DebtInstrumentAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_ConvertibleSeniorNotes0.750PercentDue2018Member" xlink:label="jhg_ConvertibleSeniorNotes0.750PercentDue2018Member"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="jhg_ConvertibleSeniorNotes0.750PercentDue2018Member" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupClassificationAxis" xlink:label="us-gaap_DisposalGroupClassificationAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_DisposalGroupClassificationAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupClassificationDomain" xlink:label="us-gaap_DisposalGroupClassificationDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DisposalGroupClassificationAxis" xlink:to="us-gaap_DisposalGroupClassificationDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" xlink:label="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DisposalGroupClassificationDomain" xlink:to="us-gaap_DiscontinuedOperationsDisposedOfBySaleMember" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:to="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_JHGBackOfficeMember" xlink:label="jhg_JHGBackOfficeMember"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:to="jhg_JHGBackOfficeMember" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:label="us-gaap_SubsequentEventLineItems"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SubsequentEventTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration" xlink:label="us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1" xlink:label="us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_DebtInstrumentConvertibleConversionRatio1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DebtInstrumentRedemptionPrincipalAmountRedeemed" xlink:label="jhg_DebtInstrumentRedemptionPrincipalAmountRedeemed"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="jhg_DebtInstrumentRedemptionPrincipalAmountRedeemed" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="us-gaap_RepaymentsOfLongTermDebt"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_RepaymentsOfLongTermDebt" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:label="us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_DebtInstrumentConvertibleConversionPrice1" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="jhg-20171231.xsd#jhg_DebtConversionConvertedInstrumentNoticeAmount" xlink:label="jhg_DebtConversionConvertedInstrumentNoticeAmount"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="jhg_DebtConversionConvertedInstrumentNoticeAmount" priority="1" use="optional"/>
<loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:label="us-gaap_CommonStockDividendsPerShareDeclared"/>
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_CommonStockDividendsPerShareDeclared" priority="1" use="optional"/>
</definitionLink>
</link:linkbase>


5 Subsequent Filings that Reference this Filing

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 2/27/24  Janus Henderson Group plc         10-K       12/31/23  130:16M                                    RDG Filings/FA
 2/28/23  Janus Henderson Group plc         10-K       12/31/22  118:22M                                    Toppan Merrill Bridge/FA
 2/25/22  Janus Henderson Group plc         10-K       12/31/21  112:21M                                    Toppan Merrill Bridge/FA
 2/24/21  Janus Henderson Group plc         10-K       12/31/20  119:23M                                    Toppan Merrill Bridge/FA
 2/16/21  Janus Henderson Group plc         8-K:5,9     2/16/21   11:256K                                   Toppan Merrill/FA
Top
Filing Submission 0001047469-18-001112   –   Alternative Formats (Word / Rich Text, HTML, Plain Text, et al.)

Copyright © 2024 Fran Finnegan & Company LLC – All Rights Reserved.
AboutPrivacyRedactionsHelp — Sat., May 11, 10:28:39.2am ET