SEC Info - Castor Maritime Inc. - ‘6-K’ for 6/30/22

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Castor Maritime Inc. – ‘6-K’ for 6/30/22 – ‘EX-101.DEF’

On: Tuesday, 8/9/22, at 9:16am ET · For: 6/30/22 · Accession #: 1140361-22-28839 · File #: 1-38802

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

 8/09/22  Castor Maritime Inc.              6-K         6/30/22   83:7.4M                                   Broadridge Fin’l So… Inc

Current, Quarterly or Annual Report by a Foreign Issuer — Form 6-K — SEA’34

Filing Table of Contents

Document/Exhibit                   Description                      Pages   Size 

 1: 6-K         Current, Quarterly or Annual Report by a Foreign    HTML     32K 
                Issuer                                                           
 2: EX-99.1     Miscellaneous Exhibit                               HTML   1.19M 
 3: EX-99.2     Miscellaneous Exhibit                               HTML    211K 
 9: R1          Document and Entity Information                     HTML     33K 
10: R2          Unaudited Interim Consolidated Balance Sheets       HTML    146K 
11: R3          Unaudited Interim Consolidated Balance Sheets       HTML     46K 
                (Parenthetical)                                                  
12: R4          Unaudited Interim Condensed Consolidated            HTML    107K 
                Statements of Comprehensive Income                               
13: R5          Unaudited Interim Condensed Consolidated            HTML     34K 
                Statements of Comprehensive Income (Parenthetical)               
14: R6          Unaudited Interim Consolidated Statements of        HTML     59K 
                Shareholders' Equity                                             
15: R7          Unaudited Interim Consolidated Statements of Cash   HTML    122K 
                Flows                                                            
16: R8          Basis of Presentation and General information       HTML     81K 
17: R9          Significant Accounting Policies and Recent          HTML     31K 
                Accounting Pronouncements                                        
18: R10         Transactions with Related Parties                   HTML     66K 
19: R11         Deferred charges, net                               HTML     30K 
20: R12         Vessels, net/ Advances for vessel acquisition/      HTML     46K 
                Vessel held for sale                                             
21: R13         Long-Term Debt                                      HTML     77K 
22: R14         Equity Capital Structure                            HTML     34K 
23: R15         Financial Instruments and Fair Value Disclosures    HTML     33K 
24: R16         Commitments and contingencies                       HTML     34K 
25: R17         Earnings Per Share                                  HTML     39K 
26: R18         Vessel Revenues                                     HTML     39K 
27: R19         Vessel Operating and Voyage Expenses                HTML     48K 
28: R20         General and Administrative Expenses                 HTML     34K 
29: R21         Interest and Finance Costs                          HTML     34K 
30: R22         Segment Information                                 HTML    124K 
31: R23         Subsequent Events                                   HTML     34K 
32: R24         Basis of Presentation and General information       HTML     28K 
                (Policies)                                                       
33: R25         Significant Accounting Policies and Recent          HTML     30K 
                Accounting Pronouncements (Policies)                             
34: R26         Basis of Presentation and General Information       HTML     76K 
                (Tables)                                                         
35: R27         Transactions with Related Parties (Tables)          HTML     46K 
36: R28         Deferred charges, net (Tables)                      HTML     29K 
37: R29         Vessels, net/ Advances for vessel acquisition/      HTML     42K 
                Vessel held for sale (Tables)                                    
38: R30         Long-Term Debt (Tables)                             HTML     63K 
39: R31         Commitments and contingencies (Tables)              HTML     28K 
40: R32         Earnings Per Share (Tables)                         HTML     36K 
41: R33         Vessel Revenues (Tables)                            HTML     33K 
42: R34         Vessel Operating and Voyage Expenses (Tables)       HTML     49K 
43: R35         General and Administrative Expenses (Tables)        HTML     33K 
44: R36         Interest and Finance Costs (Tables)                 HTML     33K 
45: R37         Segment Information (Tables)                        HTML    123K 
46: R38         Basis of Presentation and General information,      HTML     43K 
                General Information (Details)                                    
47: R39         Basis of Presentation and General information,      HTML    199K 
                Vessel Owning Subsidiaries (Details)                             
48: R40         Transactions with Related Parties, Summary          HTML     66K 
                (Details)                                                        
49: R41         Transactions with Related Parties, Pavimar          HTML     56K 
                (Details)                                                        
50: R42         Transactions with Related Parties, Thalassa         HTML     50K 
                (Details)                                                        
51: R43         Transactions with Related Parties, Castor Ships     HTML     54K 
                (Details)                                                        
52: R44         Transactions with Related Parties, Vessel           HTML     28K 
                Acquisition (Details)                                            
53: R45         Deferred charges, net (Details)                     HTML     31K 
54: R46         Vessels, net/ Advances for vessel acquisition/      HTML     50K 
                Vessel held for sale, Net Book Value (Details)                   
55: R47         Vessels, net/ Advances for vessel acquisition/      HTML     38K 
                Vessel held for sale, Vessel Acquisitions and                    
                other Capital Expenditures (Details)                             
56: R48         Vessels, net/ Advances for vessel acquisition/      HTML     27K 
                Vessel held for sale, Advances for vessel                        
                acquisition (Details)                                            
57: R49         Vessels, net/ Advances for vessel acquisition/      HTML     35K 
                Vessel held for sale, Vessel held for sale                       
                (Details)                                                        
58: R50         Long-Term Debt, Long-Term Debt Including Related    HTML     74K 
                Party Debt (Details)                                             
59: R51         Long-Term Debt, $11.0 Million Term Loan Facility    HTML     28K 
                (Details)                                                        
60: R52         Long-Term Debt, $4.5 Million Term Loan Facility     HTML     28K 
                (Details)                                                        
61: R53         Long-Term Debt, $15.29 Million Term Loan Facility   HTML     28K 
                (Details)                                                        
62: R54         Long-Term Debt, $18.0 Million Term Loan Facility    HTML     28K 
                (Details)                                                        
63: R55         Long-Term Debt, $40.75 Million Term Loan Facility   HTML     28K 
                (Details)                                                        
64: R56         Long-Term Debt, $23.15 Million Term Loan Facility   HTML     28K 
                (Details)                                                        
65: R57         Long-Term Debt, $55.0 Million Term Loan Facility    HTML     54K 
                (Details)                                                        
66: R58         Long-Term Debt, Annual Principal Payments           HTML     75K 
                (Details)                                                        
67: R59         Equity Capital Structure, Capital Stock (Details)   HTML     31K 
68: R60         Equity Capital Structure, At-the-Market Common      HTML     36K 
                Stock Offering (Details)                                         
69: R61         Equity Capital Structure, Reverse Stock Split       HTML     25K 
                (Details)                                                        
70: R62         Commitments and contingencies (Details)             HTML     54K 
71: R63         Earnings Per Share (Details)                        HTML     66K 
72: R64         Vessel Revenues (Details)                           HTML     44K 
73: R65         Vessel Operating and Voyage Expenses (Details)      HTML     49K 
74: R66         General and Administrative Expenses (Details)       HTML     33K 
75: R67         Interest and Finance Costs (Details)                HTML     35K 
76: R68         Segment Information, Information about Company's    HTML     91K 
                Reportable Segments (Details)                                    
77: R69         Segment Information, Reconciliation of Total        HTML     49K 
                Segment Assets to Total Assets (Details)                         
78: R70         Subsequent Events (Details)                         HTML     61K 
81: XML         IDEA XML File -- Filing Summary                      XML    154K 
79: XML         XBRL Instance -- brhc10040533_ex99-1_htm             XML   1.69M 
80: EXCEL       IDEA Workbook of Financial Reports                  XLSX    136K 
 5: EX-101.CAL  XBRL Calculations -- ctrm-20220630_cal               XML    189K 
 6: EX-101.DEF  XBRL Definitions -- ctrm-20220630_def                XML    837K 
 7: EX-101.LAB  XBRL Labels -- ctrm-20220630_lab                     XML   1.89M 
 8: EX-101.PRE  XBRL Presentations -- ctrm-20220630_pre              XML   1.13M 
 4: EX-101.SCH  XBRL Schema -- ctrm-20220630                         XSD    238K 
82: JSON        XBRL Instance as JSON Data -- MetaLinks              350±   528K 
83: ZIP         XBRL Zipped Folder -- 0001140361-22-028839-xbrl      Zip    280K

‘EX-101.DEF’ — XBRL Definitions — ctrm-20220630_def

This Exhibit is an XBRL XML File.

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<link:roleRef roleURI="http://castormaritime.com/role/EquityCapitalStructureAtthemarketCommonStockOfferingDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#EquityCapitalStructureAtthemarketCommonStockOfferingDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/EquityCapitalStructureCapitalStockDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#EquityCapitalStructureCapitalStockDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebtAnnualPrincipalPaymentsDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebtAnnualPrincipalPaymentsDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebt550MillionTermLoanFacilityDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebt550MillionTermLoanFacilityDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebt2315MillionTermLoanFacilityDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebt2315MillionTermLoanFacilityDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebt4075MillionTermLoanFacilityDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebt4075MillionTermLoanFacilityDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebt180MillionTermLoanFacilityDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebt180MillionTermLoanFacilityDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebt1529MillionTermLoanFacilityDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebt1529MillionTermLoanFacilityDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebt45MillionTermLoanFacilityDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebt45MillionTermLoanFacilityDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebt110MillionTermLoanFacilityDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebt110MillionTermLoanFacilityDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebtLongtermDebtIncludingRelatedPartyDebtDetailsCalc2" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebtLongtermDebtIncludingRelatedPartyDebtDetailsCalc2"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebtLongtermDebtIncludingRelatedPartyDebtDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebtLongtermDebtIncludingRelatedPartyDebtDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleVesselHeldForSaleDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleVesselHeldForSaleDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleAdvancesForVesselAcquisitionDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleAdvancesForVesselAcquisitionDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleVesselAcquisitionsAndOtherCapitalExpendituresDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleVesselAcquisitionsAndOtherCapitalExpendituresDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleNetBookValueDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleNetBookValueDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/DeferredChargesNetDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#DeferredChargesNetDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/TransactionsWithRelatedPartiesVesselAcquisitionDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#TransactionsWithRelatedPartiesVesselAcquisitionDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/TransactionsWithRelatedPartiesCastorShipsDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#TransactionsWithRelatedPartiesCastorShipsDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/TransactionsWithRelatedPartiesThalassaDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#TransactionsWithRelatedPartiesThalassaDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/TransactionsWithRelatedPartiesPavimarDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#TransactionsWithRelatedPartiesPavimarDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/TransactionsWithRelatedPartiesSummaryDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#TransactionsWithRelatedPartiesSummaryDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationVesselOwningSubsidiariesDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#BasisOfPresentationAndGeneralInformationVesselOwningSubsidiariesDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationGeneralInformationDetails" xlink:type="simple" xlink:href="ctrm-20220630.xsd#BasisOfPresentationAndGeneralInformationGeneralInformationDetails"/>

<link:roleRef roleURI="http://castormaritime.com/role/SegmentInformationTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#SegmentInformationTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/InterestAndFinanceCostsTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#InterestAndFinanceCostsTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/GeneralAndAdministrativeExpensesTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#GeneralAndAdministrativeExpensesTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/VesselOperatingAndVoyageExpensesTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#VesselOperatingAndVoyageExpensesTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/VesselRevenuesTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#VesselRevenuesTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/EarningsPerShareTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#EarningsPerShareTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/CommitmentsAndContingenciesTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#CommitmentsAndContingenciesTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/LongtermDebtTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#LongtermDebtTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/DeferredChargesNetTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#DeferredChargesNetTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/TransactionsWithRelatedPartiesTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#TransactionsWithRelatedPartiesTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationTables" xlink:type="simple" xlink:href="ctrm-20220630.xsd#BasisOfPresentationAndGeneralInformationTables"/>

<link:roleRef roleURI="http://castormaritime.com/role/SignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies" xlink:type="simple" xlink:href="ctrm-20220630.xsd#SignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies"/>

<link:roleRef roleURI="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationPolicies" xlink:type="simple" xlink:href="ctrm-20220630.xsd#BasisOfPresentationAndGeneralInformationPolicies"/>

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<link:roleRef roleURI="http://castormaritime.com/role/SegmentInformation" xlink:type="simple" xlink:href="ctrm-20220630.xsd#SegmentInformation"/>

<link:roleRef roleURI="http://castormaritime.com/role/InterestAndFinanceCosts" xlink:type="simple" xlink:href="ctrm-20220630.xsd#InterestAndFinanceCosts"/>

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<link:roleRef roleURI="http://castormaritime.com/role/UnauditedInterimConsolidatedStatementsOfCashFlows" xlink:type="simple" xlink:href="ctrm-20220630.xsd#UnauditedInterimConsolidatedStatementsOfCashFlows"/>

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<link:roleRef roleURI="http://castormaritime.com/role/UnauditedInterimCondensedConsolidatedStatementsOfComprehensiveIncomeParenthetical" xlink:type="simple" xlink:href="ctrm-20220630.xsd#UnauditedInterimCondensedConsolidatedStatementsOfComprehensiveIncomeParenthetical"/>

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<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/UnauditedInterimConsolidatedBalanceSheets">

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="PreferredStockParOrStatedValuePerShare" xlink:title="PreferredStockParOrStatedValuePerShare"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockParOrStatedValuePerShare" xlink:title="definition: StatementLineItems to PreferredStockParOrStatedValuePerShare" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="PreferredStockSharesAuthorized" xlink:title="PreferredStockSharesAuthorized"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesAuthorized" xlink:title="definition: StatementLineItems to PreferredStockSharesAuthorized" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="PreferredStockSharesIssued" xlink:title="PreferredStockSharesIssued"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesIssued" xlink:title="definition: StatementLineItems to PreferredStockSharesIssued" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="PreferredStockSharesOutstanding" xlink:title="PreferredStockSharesOutstanding"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="PreferredStockSharesOutstanding" xlink:title="definition: StatementLineItems to PreferredStockSharesOutstanding" order="11.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="AssetsNoncurrentAbstract" xlink:title="definition: StatementLineItems to AssetsNoncurrentAbstract" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionSaleAndPurchaseCommission" xlink:label="RelatedPartyTransactionSaleAndPurchaseCommission" xlink:title="RelatedPartyTransactionSaleAndPurchaseCommission"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="RelatedPartyTransactionSaleAndPurchaseCommission" xlink:title="definition: StatementLineItems to RelatedPartyTransactionSaleAndPurchaseCommission" order="13.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="14.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesBPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesBPreferredStockMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/UnauditedInterimCondensedConsolidatedStatementsOfComprehensiveIncome"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/UnauditedInterimCondensedConsolidatedStatementsOfComprehensiveIncomeParenthetical"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/UnauditedInterimConsolidatedStatementsOfShareholdersEquity">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="IncreaseDecreaseInStockholdersEquityRollForward"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="definition: StatementLineItems to IncreaseDecreaseInStockholdersEquityRollForward" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockholdersEquity" xlink:title="definition: StatementLineItems to StockholdersEquity" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding" xlink:label="SharesOutstanding" xlink:title="SharesOutstanding"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="SharesOutstanding" xlink:title="definition: StatementLineItems to SharesOutstanding" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StockIssuedDuringPeriodValueNewIssuesRegisteredDirectOfferings" xlink:label="StockIssuedDuringPeriodValueNewIssuesRegisteredDirectOfferings" xlink:title="StockIssuedDuringPeriodValueNewIssuesRegisteredDirectOfferings"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueNewIssuesRegisteredDirectOfferings" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueNewIssuesRegisteredDirectOfferings" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StockIssuedDuringPeriodSharesNewIssuesRegisteredDirectOfferings" xlink:label="StockIssuedDuringPeriodSharesNewIssuesRegisteredDirectOfferings" xlink:title="StockIssuedDuringPeriodSharesNewIssuesRegisteredDirectOfferings"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesNewIssuesRegisteredDirectOfferings" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesNewIssuesRegisteredDirectOfferings" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StockIssuedDuringPeriodValueExerciseOfWarrants" xlink:label="StockIssuedDuringPeriodValueExerciseOfWarrants" xlink:title="StockIssuedDuringPeriodValueExerciseOfWarrants"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueExerciseOfWarrants" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueExerciseOfWarrants" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StockIssuedDuringPeriodSharesExerciseOfWarrants" xlink:label="StockIssuedDuringPeriodSharesExerciseOfWarrants" xlink:title="StockIssuedDuringPeriodSharesExerciseOfWarrants"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesExerciseOfWarrants" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesExerciseOfWarrants" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StockIssuedDuringPeriodValueNewIssuesAtTheMarketOffering" xlink:label="StockIssuedDuringPeriodValueNewIssuesAtTheMarketOffering" xlink:title="StockIssuedDuringPeriodValueNewIssuesAtTheMarketOffering"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodValueNewIssuesAtTheMarketOffering" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodValueNewIssuesAtTheMarketOffering" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StockIssuedDuringPeriodSharesNewIssuesAtTheMarketOffering" xlink:label="StockIssuedDuringPeriodSharesNewIssuesAtTheMarketOffering" xlink:title="StockIssuedDuringPeriodSharesNewIssuesAtTheMarketOffering"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="StockIssuedDuringPeriodSharesNewIssuesAtTheMarketOffering" xlink:title="definition: StatementLineItems to StockIssuedDuringPeriodSharesNewIssuesAtTheMarketOffering" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:label="NetIncomeLoss" xlink:title="NetIncomeLoss"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="StatementLineItems" xlink:to="NetIncomeLoss" xlink:title="definition: StatementLineItems to NetIncomeLoss" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="StatementTable" xlink:title="StatementTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="StatementLineItems" xlink:to="StatementTable" xlink:title="definition: StatementLineItems to StatementTable" order="11.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="StatementTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: StatementTable to StatementEquityComponentsAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_2" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember" xlink:title="CommonStockMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="CommonStockMember" xlink:title="definition: EquityComponentDomain to CommonStockMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PreferredStockMember" xlink:label="PreferredStockMember" xlink:title="PreferredStockMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="PreferredStockMember" xlink:title="definition: EquityComponentDomain to PreferredStockMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ParValueOfSharesIssuedMember" xlink:label="ParValueOfSharesIssuedMember" xlink:title="ParValueOfSharesIssuedMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="ParValueOfSharesIssuedMember" xlink:title="definition: EquityComponentDomain to ParValueOfSharesIssuedMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="AdditionalPaidInCapitalMember" xlink:title="AdditionalPaidInCapitalMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="AdditionalPaidInCapitalMember" xlink:title="definition: EquityComponentDomain to AdditionalPaidInCapitalMember" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember" xlink:label="RetainedEarningsMember" xlink:title="RetainedEarningsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EquityComponentDomain" xlink:to="RetainedEarningsMember" xlink:title="definition: EquityComponentDomain to RetainedEarningsMember" order="5.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesBPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesBPreferredStockMember" order="2.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/UnauditedInterimConsolidatedStatementsOfCashFlows"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformation"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SignificantAccountingPoliciesAndRecentAccountingPronouncements"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/TransactionsWithRelatedParties"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/DeferredChargesNet"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSale"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/EquityCapitalStructure"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/FinancialInstrumentsAndFairValueDisclosures"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/CommitmentsAndContingencies"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/EarningsPerShare"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselRevenues"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselOperatingAndVoyageExpenses"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/GeneralAndAdministrativeExpenses"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/InterestAndFinanceCosts"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SegmentInformation"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SubsequentEvents"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationPolicies"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/TransactionsWithRelatedPartiesTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/DeferredChargesNetTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebtTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/CommitmentsAndContingenciesTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/EarningsPerShareTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselRevenuesTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselOperatingAndVoyageExpensesTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/GeneralAndAdministrativeExpensesTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/InterestAndFinanceCostsTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SegmentInformationTables"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationGeneralInformationDetails">

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_OrganizationLineItems" xlink:label="OrganizationLineItems" xlink:title="OrganizationLineItems"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_BasisOfPresentationAndOrganizationAbstract" xlink:label="BasisOfPresentationAndOrganizationAbstract" xlink:title="BasisOfPresentationAndOrganizationAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="BasisOfPresentationAndOrganizationAbstract" xlink:title="definition: OrganizationLineItems to BasisOfPresentationAndOrganizationAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PercentageOfSharesHeld" xlink:label="PercentageOfSharesHeld" xlink:title="PercentageOfSharesHeld"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="PercentageOfSharesHeld" xlink:title="definition: OrganizationLineItems to PercentageOfSharesHeld" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVessels" xlink:label="NumberOfVessels" xlink:title="NumberOfVessels"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="NumberOfVessels" xlink:title="definition: OrganizationLineItems to NumberOfVessels" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselDeadWeightTonnage" xlink:label="VesselDeadWeightTonnage" xlink:title="VesselDeadWeightTonnage"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="VesselDeadWeightTonnage" xlink:title="definition: OrganizationLineItems to VesselDeadWeightTonnage" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_OrganizationTable" xlink:label="OrganizationTable" xlink:title="OrganizationTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="OrganizationLineItems" xlink:to="OrganizationTable" xlink:title="definition: OrganizationLineItems to OrganizationTable" order="5.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis" xlink:label="LegalEntityAxis" xlink:title="LegalEntityAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="OrganizationTable" xlink:to="LegalEntityAxis" xlink:title="definition: OrganizationTable to LegalEntityAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain" xlink:label="EntityDomain" xlink:title="EntityDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="LegalEntityAxis" xlink:to="EntityDomain" xlink:title="definition: LegalEntityAxis to EntityDomain" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain" xlink:label="EntityDomain_2" xlink:title="EntityDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LegalEntityAxis" xlink:to="EntityDomain_2" xlink:title="definition: LegalEntityAxis to EntityDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ThalassaInvestmentCoSAMember" xlink:label="ThalassaInvestmentCoSAMember" xlink:title="ThalassaInvestmentCoSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="EntityDomain" xlink:to="ThalassaInvestmentCoSAMember" xlink:title="definition: EntityDomain to ThalassaInvestmentCoSAMember" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="OrganizationTable" xlink:to="StatementClassOfStockAxis" xlink:title="definition: OrganizationTable to StatementClassOfStockAxis" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="SeriesBPreferredStockMember" xlink:title="definition: ClassOfStockDomain to SeriesBPreferredStockMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="OrganizationTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: OrganizationTable to PropertyPlantAndEquipmentByTypeAxis" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CapesizeVesselMember" xlink:label="CapesizeVesselMember" xlink:title="CapesizeVesselMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="CapesizeVesselMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to CapesizeVesselMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_KamsarmaxVesselMember" xlink:label="KamsarmaxVesselMember" xlink:title="KamsarmaxVesselMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="KamsarmaxVesselMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to KamsarmaxVesselMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PanamaxVesselMember" xlink:label="PanamaxVesselMember" xlink:title="PanamaxVesselMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="PanamaxVesselMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to PanamaxVesselMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_AframaxMember" xlink:label="AframaxMember" xlink:title="AframaxMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="AframaxMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to AframaxMember" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_AframaxLr2TankerMember" xlink:label="AframaxLr2TankerMember" xlink:title="AframaxLr2TankerMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="AframaxLr2TankerMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to AframaxLr2TankerMember" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_Mr1Member" xlink:label="Mr1Member" xlink:title="Mr1Member"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="Mr1Member" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to Mr1Member" order="6.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/BasisOfPresentationAndGeneralInformationVesselOwningSubsidiariesDetails">

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_OrganizationLineItems" xlink:label="OrganizationLineItems" xlink:title="OrganizationLineItems"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SubsidiariesInConsolidationAbstract" xlink:label="SubsidiariesInConsolidationAbstract" xlink:title="SubsidiariesInConsolidationAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="SubsidiariesInConsolidationAbstract" xlink:title="definition: OrganizationLineItems to SubsidiariesInConsolidationAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityIncorporationStateCountryCode" xlink:label="EntityIncorporationStateCountryCode" xlink:title="EntityIncorporationStateCountryCode"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="EntityIncorporationStateCountryCode" xlink:title="definition: OrganizationLineItems to EntityIncorporationStateCountryCode" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselName" xlink:label="VesselName" xlink:title="VesselName"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="VesselName" xlink:title="definition: OrganizationLineItems to VesselName" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselDeadWeightTonnage" xlink:label="VesselDeadWeightTonnage" xlink:title="VesselDeadWeightTonnage"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="VesselDeadWeightTonnage" xlink:title="definition: OrganizationLineItems to VesselDeadWeightTonnage" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselYearBuilt" xlink:label="VesselYearBuilt" xlink:title="VesselYearBuilt"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="VesselYearBuilt" xlink:title="definition: OrganizationLineItems to VesselYearBuilt" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselDeliveryDateMonthAndYear" xlink:label="VesselDeliveryDateMonthAndYear" xlink:title="VesselDeliveryDateMonthAndYear"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="VesselDeliveryDateMonthAndYear" xlink:title="definition: OrganizationLineItems to VesselDeliveryDateMonthAndYear" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PropertyPlantAndEquipmentSalesPrice" xlink:label="PropertyPlantAndEquipmentSalesPrice" xlink:title="PropertyPlantAndEquipmentSalesPrice"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="OrganizationLineItems" xlink:to="PropertyPlantAndEquipmentSalesPrice" xlink:title="definition: OrganizationLineItems to PropertyPlantAndEquipmentSalesPrice" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_OrganizationTable" xlink:label="OrganizationTable" xlink:title="OrganizationTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="OrganizationLineItems" xlink:to="OrganizationTable" xlink:title="definition: OrganizationLineItems to OrganizationTable" order="8.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="ConsolidatedEntitiesAxis" xlink:title="ConsolidatedEntitiesAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="OrganizationTable" xlink:to="ConsolidatedEntitiesAxis" xlink:title="definition: OrganizationTable to ConsolidatedEntitiesAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="ConsolidatedEntitiesDomain" xlink:title="ConsolidatedEntitiesDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ConsolidatedEntitiesAxis" xlink:to="ConsolidatedEntitiesDomain" xlink:title="definition: ConsolidatedEntitiesAxis to ConsolidatedEntitiesDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ConsolidatedEntitiesAxis" xlink:to="ConsolidatedEntitiesDomain_2" xlink:title="definition: ConsolidatedEntitiesAxis to ConsolidatedEntitiesDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SpetsesShippingCoMember" xlink:label="SpetsesShippingCoMember" xlink:title="SpetsesShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="SpetsesShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to SpetsesShippingCoMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_BistroMaritimeCoMember" xlink:label="BistroMaritimeCoMember" xlink:title="BistroMaritimeCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="BistroMaritimeCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to BistroMaritimeCoMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PikachuShippingCoMember" xlink:label="PikachuShippingCoMember" xlink:title="PikachuShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="PikachuShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to PikachuShippingCoMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_BagheeraShippingCoMember" xlink:label="BagheeraShippingCoMember" xlink:title="BagheeraShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="BagheeraShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to BagheeraShippingCoMember" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PocahontasShippingCoMember" xlink:label="PocahontasShippingCoMember" xlink:title="PocahontasShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="PocahontasShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to PocahontasShippingCoMember" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_JumaruShippingCoMember" xlink:label="JumaruShippingCoMember" xlink:title="JumaruShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="JumaruShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to JumaruShippingCoMember" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SuperMarioShippingCoMember" xlink:label="SuperMarioShippingCoMember" xlink:title="SuperMarioShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="SuperMarioShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to SuperMarioShippingCoMember" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PumbaShippingCoMember" xlink:label="PumbaShippingCoMember" xlink:title="PumbaShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="PumbaShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to PumbaShippingCoMember" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_KabamaruShippingCoMember" xlink:label="KabamaruShippingCoMember" xlink:title="KabamaruShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="KabamaruShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to KabamaruShippingCoMember" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_LuffyShippingCoMember" xlink:label="LuffyShippingCoMember" xlink:title="LuffyShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="LuffyShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to LuffyShippingCoMember" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_LionoShippingCoMember" xlink:label="LionoShippingCoMember" xlink:title="LionoShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="LionoShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to LionoShippingCoMember" order="11.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StewieShippingCoMember" xlink:label="StewieShippingCoMember" xlink:title="StewieShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="StewieShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to StewieShippingCoMember" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SnoopyShippingCoMember" xlink:label="SnoopyShippingCoMember" xlink:title="SnoopyShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="SnoopyShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to SnoopyShippingCoMember" order="13.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MulanShippingCoMember" xlink:label="MulanShippingCoMember" xlink:title="MulanShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="MulanShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to MulanShippingCoMember" order="14.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CinderellaShippingCoMember" xlink:label="CinderellaShippingCoMember" xlink:title="CinderellaShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="CinderellaShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to CinderellaShippingCoMember" order="15.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RocketShippingCoMember" xlink:label="RocketShippingCoMember" xlink:title="RocketShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="RocketShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to RocketShippingCoMember" order="16.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_GamoraShippingCoMember" xlink:label="GamoraShippingCoMember" xlink:title="GamoraShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="GamoraShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to GamoraShippingCoMember" order="17.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_StarlordShippingCoMember" xlink:label="StarlordShippingCoMember" xlink:title="StarlordShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="StarlordShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to StarlordShippingCoMember" order="18.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_HawkeyeShippingCoMember" xlink:label="HawkeyeShippingCoMember" xlink:title="HawkeyeShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="HawkeyeShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to HawkeyeShippingCoMember" order="19.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ElektraShippingCoMember" xlink:label="ElektraShippingCoMember" xlink:title="ElektraShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="ElektraShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to ElektraShippingCoMember" order="20.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VisionShippingCoMember" xlink:label="VisionShippingCoMember" xlink:title="VisionShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="VisionShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to VisionShippingCoMember" order="21.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ColossusShippingCoMember" xlink:label="ColossusShippingCoMember" xlink:title="ColossusShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="ColossusShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to ColossusShippingCoMember" order="22.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_XavierShippingCoMember" xlink:label="XavierShippingCoMember" xlink:title="XavierShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="XavierShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to XavierShippingCoMember" order="23.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SongokuShippingCoMember" xlink:label="SongokuShippingCoMember" xlink:title="SongokuShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="SongokuShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to SongokuShippingCoMember" order="24.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_AsterixShippingCoMember" xlink:label="AsterixShippingCoMember" xlink:title="AsterixShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="AsterixShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to AsterixShippingCoMember" order="25.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_JohnnyBravoShippingCoMember" xlink:label="JohnnyBravoShippingCoMember" xlink:title="JohnnyBravoShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="JohnnyBravoShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to JohnnyBravoShippingCoMember" order="26.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_GarfieldShippingCoMember" xlink:label="GarfieldShippingCoMember" xlink:title="GarfieldShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="GarfieldShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to GarfieldShippingCoMember" order="27.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DraxShippingCoMember" xlink:label="DraxShippingCoMember" xlink:title="DraxShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="DraxShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to DraxShippingCoMember" order="28.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MickeyShippingCoMember" xlink:label="MickeyShippingCoMember" xlink:title="MickeyShippingCoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="MickeyShippingCoMember" xlink:title="definition: ConsolidatedEntitiesDomain to MickeyShippingCoMember" order="29.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CastorMaritimeScrCorpMember" xlink:label="CastorMaritimeScrCorpMember" xlink:title="CastorMaritimeScrCorpMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidatedEntitiesDomain" xlink:to="CastorMaritimeScrCorpMember" xlink:title="definition: ConsolidatedEntitiesDomain to CastorMaritimeScrCorpMember" order="30.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="OrganizationTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: OrganizationTable to PropertyPlantAndEquipmentByTypeAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicPMember" xlink:label="MagicPMember" xlink:title="MagicPMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicPMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicPMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicSunMember" xlink:label="MagicSunMember" xlink:title="MagicSunMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicSunMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicSunMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicMoonMember" xlink:label="MagicMoonMember" xlink:title="MagicMoonMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicMoonMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicMoonMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicRainbowMember" xlink:label="MagicRainbowMember" xlink:title="MagicRainbowMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicRainbowMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicRainbowMember" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicHorizonMember" xlink:label="MagicHorizonMember" xlink:title="MagicHorizonMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicHorizonMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicHorizonMember" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicNovaMember" xlink:label="MagicNovaMember" xlink:title="MagicNovaMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicNovaMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicNovaMember" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicVenusMember" xlink:label="MagicVenusMember" xlink:title="MagicVenusMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicVenusMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicVenusMember" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicOrionMember" xlink:label="MagicOrionMember" xlink:title="MagicOrionMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicOrionMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicOrionMember" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicArgoMember" xlink:label="MagicArgoMember" xlink:title="MagicArgoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicArgoMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicArgoMember" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicTwilightMember" xlink:label="MagicTwilightMember" xlink:title="MagicTwilightMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicTwilightMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicTwilightMember" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicThunderMember" xlink:label="MagicThunderMember" xlink:title="MagicThunderMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicThunderMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicThunderMember" order="11.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicVelaMember" xlink:label="MagicVelaMember" xlink:title="MagicVelaMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicVelaMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicVelaMember" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicNebulaMember" xlink:label="MagicNebulaMember" xlink:title="MagicNebulaMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicNebulaMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicNebulaMember" order="13.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicStarlightMember" xlink:label="MagicStarlightMember" xlink:title="MagicStarlightMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicStarlightMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicStarlightMember" order="14.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicEclipseMember" xlink:label="MagicEclipseMember" xlink:title="MagicEclipseMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicEclipseMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicEclipseMember" order="15.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderPolarisMember" xlink:label="WonderPolarisMember" xlink:title="WonderPolarisMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderPolarisMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderPolarisMember" order="16.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderSiriusMember" xlink:label="WonderSiriusMember" xlink:title="WonderSiriusMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderSiriusMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderSiriusMember" order="17.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderVegaMember" xlink:label="WonderVegaMember" xlink:title="WonderVegaMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderVegaMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderVegaMember" order="18.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderAviorMember" xlink:label="WonderAviorMember" xlink:title="WonderAviorMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderAviorMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderAviorMember" order="19.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderArcturusMember" xlink:label="WonderArcturusMember" xlink:title="WonderArcturusMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderArcturusMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderArcturusMember" order="20.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderMimosaMember" xlink:label="WonderMimosaMember" xlink:title="WonderMimosaMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderMimosaMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderMimosaMember" order="21.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderMusicaMember" xlink:label="WonderMusicaMember" xlink:title="WonderMusicaMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderMusicaMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderMusicaMember" order="22.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderFormosaMember" xlink:label="WonderFormosaMember" xlink:title="WonderFormosaMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderFormosaMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderFormosaMember" order="23.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicPlutoMember" xlink:label="MagicPlutoMember" xlink:title="MagicPlutoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicPlutoMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicPlutoMember" order="24.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicPerseusMember" xlink:label="MagicPerseusMember" xlink:title="MagicPerseusMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicPerseusMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicPerseusMember" order="25.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicMarsMember" xlink:label="MagicMarsMember" xlink:title="MagicMarsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicMarsMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicMarsMember" order="26.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicPhoenixMember" xlink:label="MagicPhoenixMember" xlink:title="MagicPhoenixMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicPhoenixMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicPhoenixMember" order="27.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderBellatrixMember" xlink:label="WonderBellatrixMember" xlink:title="WonderBellatrixMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderBellatrixMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderBellatrixMember" order="28.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicCallistoMember" xlink:label="MagicCallistoMember" xlink:title="MagicCallistoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicCallistoMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicCallistoMember" order="29.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/TransactionsWithRelatedPartiesSummaryDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="RelatedPartyTransactionLineItems" xlink:title="RelatedPartyTransactionLineItems"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionDueFromToRelatedPartyCurrentAbstract" xlink:label="RelatedPartyTransactionDueFromToRelatedPartyCurrentAbstract" xlink:title="RelatedPartyTransactionDueFromToRelatedPartyCurrentAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionDueFromToRelatedPartyCurrentAbstract" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionDueFromToRelatedPartyCurrentAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionDueFromToRelatedPartyAbstract" xlink:label="RelatedPartyTransactionDueFromToRelatedPartyAbstract" xlink:title="RelatedPartyTransactionDueFromToRelatedPartyAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionDueFromToRelatedPartyAbstract" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionDueFromToRelatedPartyAbstract" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract" xlink:label="AssetsAbstract" xlink:title="AssetsAbstract"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAbstract" xlink:label="LiabilitiesAbstract" xlink:title="LiabilitiesAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="LiabilitiesAbstract" xlink:title="definition: RelatedPartyTransactionLineItems to LiabilitiesAbstract" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DueToRelatedPartiesCurrent" xlink:label="DueToRelatedPartiesCurrent" xlink:title="DueToRelatedPartiesCurrent"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DueToRelatedPartiesCurrent" xlink:title="definition: RelatedPartyTransactionLineItems to DueToRelatedPartiesCurrent" order="5.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="AccountsPayableRelatedPartiesCurrent" xlink:title="definition: RelatedPartyTransactionLineItems to AccountsPayableRelatedPartiesCurrent" order="6.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DueFromRelatedPartiesNoncurrent" xlink:title="definition: RelatedPartyTransactionLineItems to DueFromRelatedPartiesNoncurrent" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionManagementFees" xlink:label="RelatedPartyTransactionManagementFees" xlink:title="RelatedPartyTransactionManagementFees"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionManagementFees" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionManagementFees" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionCommissions" xlink:label="RelatedPartyTransactionCommissions" xlink:title="RelatedPartyTransactionCommissions"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionCommissions" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionCommissions" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseRelatedParty" xlink:label="InterestExpenseRelatedParty" xlink:title="InterestExpenseRelatedParty"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="InterestExpenseRelatedParty" xlink:title="definition: RelatedPartyTransactionLineItems to InterestExpenseRelatedParty" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" xlink:label="RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" xlink:title="RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" order="11.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionSaleAndPurchaseCommission" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionSaleAndPurchaseCommission" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="13.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="RelatedPartyTransactionsByRelatedPartyAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionsByRelatedPartyAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain" xlink:title="RelatedPartyDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain_2" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PavimarSAMember" xlink:label="PavimarSAMember" xlink:title="PavimarSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="PavimarSAMember" xlink:title="definition: RelatedPartyDomain to PavimarSAMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ThalassaInvestmentCoSAMember" xlink:label="ThalassaInvestmentCoSAMember" xlink:title="ThalassaInvestmentCoSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="ThalassaInvestmentCoSAMember" xlink:title="definition: RelatedPartyDomain to ThalassaInvestmentCoSAMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CastorShipsSAMember" xlink:label="CastorShipsSAMember" xlink:title="CastorShipsSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="CastorShipsSAMember" xlink:title="definition: RelatedPartyDomain to CastorShipsSAMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:label="DebtInstrumentAxis" xlink:title="DebtInstrumentAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="DebtInstrumentAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to DebtInstrumentAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="DebtInstrumentNameDomain" xlink:title="DebtInstrumentNameDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="DebtInstrumentAxis" xlink:to="DebtInstrumentNameDomain" xlink:title="definition: DebtInstrumentAxis to DebtInstrumentNameDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DebtInstrumentAxis" xlink:to="DebtInstrumentNameDomain_2" xlink:title="definition: DebtInstrumentAxis to DebtInstrumentNameDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_TermLoanFacilityMember" xlink:label="TermLoanFacilityMember" xlink:title="TermLoanFacilityMember"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="RelatedPartyTransactionAxis" xlink:title="RelatedPartyTransactionAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionAxis" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="RelatedPartyTransactionDomain" xlink:title="RelatedPartyTransactionDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RelatedPartyTransactionAxis" xlink:to="RelatedPartyTransactionDomain" xlink:title="definition: RelatedPartyTransactionAxis to RelatedPartyTransactionDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionAxis" xlink:to="RelatedPartyTransactionDomain_2" xlink:title="definition: RelatedPartyTransactionAxis to RelatedPartyTransactionDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselManagementAgreementsMember" xlink:label="VesselManagementAgreementsMember" xlink:title="VesselManagementAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionDomain" xlink:to="VesselManagementAgreementsMember" xlink:title="definition: RelatedPartyTransactionDomain to VesselManagementAgreementsMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CommercialManagementServicesMember" xlink:label="CommercialManagementServicesMember" xlink:title="CommercialManagementServicesMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionDomain" xlink:to="CommercialManagementServicesMember" xlink:title="definition: RelatedPartyTransactionDomain to CommercialManagementServicesMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to IncomeStatementLocationAxis" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_2" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VoyageExpensesMember" xlink:label="VoyageExpensesMember" xlink:title="VoyageExpensesMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="VoyageExpensesMember" xlink:title="definition: IncomeStatementLocationDomain to VoyageExpensesMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseMember" xlink:label="InterestExpenseMember" xlink:title="InterestExpenseMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="InterestExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to InterestExpenseMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="GeneralAndAdministrativeExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to GeneralAndAdministrativeExpenseMember" order="3.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/TransactionsWithRelatedPartiesPavimarDetails">

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionFixedDailyFee" xlink:label="RelatedPartyTransactionFixedDailyFee" xlink:title="RelatedPartyTransactionFixedDailyFee"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionFixedDailyFee" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionFixedDailyFee" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsUnderTechnicalManagement" xlink:label="NumberOfVesselsUnderTechnicalManagement" xlink:title="NumberOfVesselsUnderTechnicalManagement"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="NumberOfVesselsUnderTechnicalManagement" xlink:title="definition: RelatedPartyTransactionLineItems to NumberOfVesselsUnderTechnicalManagement" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsUnderOperationalManagement" xlink:label="NumberOfVesselsUnderOperationalManagement" xlink:title="NumberOfVesselsUnderOperationalManagement"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="NumberOfVesselsUnderOperationalManagement" xlink:title="definition: RelatedPartyTransactionLineItems to NumberOfVesselsUnderOperationalManagement" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WorkingCapitalGuaranteeDeposits" xlink:label="WorkingCapitalGuaranteeDeposits" xlink:title="WorkingCapitalGuaranteeDeposits"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="WorkingCapitalGuaranteeDeposits" xlink:title="definition: RelatedPartyTransactionLineItems to WorkingCapitalGuaranteeDeposits" order="5.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DueToRelatedPartiesCurrent" xlink:title="definition: RelatedPartyTransactionLineItems to DueToRelatedPartiesCurrent" order="6.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DueFromRelatedPartiesNoncurrent" xlink:title="definition: RelatedPartyTransactionLineItems to DueFromRelatedPartiesNoncurrent" order="7.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionManagementFees" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionManagementFees" order="8.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="9.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PavimarSAMember" xlink:label="PavimarSAMember" xlink:title="PavimarSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_TechnicalShipmanagementAgreementsMember" xlink:label="TechnicalShipmanagementAgreementsMember" xlink:title="TechnicalShipmanagementAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionDomain" xlink:to="TechnicalShipmanagementAgreementsMember" xlink:title="definition: RelatedPartyTransactionDomain to TechnicalShipmanagementAgreementsMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SubcontractedManagementAgreementsMember" xlink:label="SubcontractedManagementAgreementsMember" xlink:title="SubcontractedManagementAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionDomain" xlink:to="SubcontractedManagementAgreementsMember" xlink:title="definition: RelatedPartyTransactionDomain to SubcontractedManagementAgreementsMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WorkingCapitalAdvancesMember" xlink:label="WorkingCapitalAdvancesMember" xlink:title="WorkingCapitalAdvancesMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionDomain" xlink:to="WorkingCapitalAdvancesMember" xlink:title="definition: RelatedPartyTransactionDomain to WorkingCapitalAdvancesMember" order="4.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to PropertyPlantAndEquipmentByTypeAxis" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DryBulkCarrierMember" xlink:label="DryBulkCarrierMember" xlink:title="DryBulkCarrierMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="DryBulkCarrierMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to DryBulkCarrierMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_TankerMember" xlink:label="TankerMember" xlink:title="TankerMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="TankerMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to TankerMember" order="2.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/TransactionsWithRelatedPartiesThalassaDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="DebtInstrumentFaceAmount" xlink:title="DebtInstrumentFaceAmount"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: RelatedPartyTransactionLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromRelatedPartyDebt" xlink:label="ProceedsFromRelatedPartyDebt" xlink:title="ProceedsFromRelatedPartyDebt"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ProceedsFromRelatedPartyDebt" xlink:title="definition: RelatedPartyTransactionLineItems to ProceedsFromRelatedPartyDebt" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="DebtInstrumentInterestRateStatedPercentage" xlink:title="DebtInstrumentInterestRateStatedPercentage"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DebtInstrumentInterestRateStatedPercentage" xlink:title="definition: RelatedPartyTransactionLineItems to DebtInstrumentInterestRateStatedPercentage" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DebtInstrumentTermOfExtension" xlink:label="DebtInstrumentTermOfExtension" xlink:title="DebtInstrumentTermOfExtension"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DebtInstrumentTermOfExtension" xlink:title="definition: RelatedPartyTransactionLineItems to DebtInstrumentTermOfExtension" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="DebtInstrumentMaturityDate" xlink:title="DebtInstrumentMaturityDate"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="DebtInstrumentMaturityDate" xlink:title="definition: RelatedPartyTransactionLineItems to DebtInstrumentMaturityDate" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfRelatedPartyDebt" xlink:label="RepaymentsOfRelatedPartyDebt" xlink:title="RepaymentsOfRelatedPartyDebt"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RepaymentsOfRelatedPartyDebt" xlink:title="definition: RelatedPartyTransactionLineItems to RepaymentsOfRelatedPartyDebt" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_AccruedInterestRelatedPartiesCurrent" xlink:label="AccruedInterestRelatedPartiesCurrent" xlink:title="AccruedInterestRelatedPartiesCurrent"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="AccruedInterestRelatedPartiesCurrent" xlink:title="definition: RelatedPartyTransactionLineItems to AccruedInterestRelatedPartiesCurrent" order="8.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="InterestExpenseRelatedParty" xlink:title="definition: RelatedPartyTransactionLineItems to InterestExpenseRelatedParty" order="9.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="10.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ThalassaInvestmentCoSAMember" xlink:label="ThalassaInvestmentCoSAMember" xlink:title="ThalassaInvestmentCoSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="DebtInstrumentAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to DebtInstrumentAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_TermLoanFacilityMember" xlink:label="TermLoanFacilityMember" xlink:title="TermLoanFacilityMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to IncomeStatementLocationAxis" order="3.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="InterestExpenseMember" xlink:title="definition: IncomeStatementLocationDomain to InterestExpenseMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/TransactionsWithRelatedPartiesCastorShipsDetails">

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionQuarterlyManagementFee" xlink:label="RelatedPartyTransactionQuarterlyManagementFee" xlink:title="RelatedPartyTransactionQuarterlyManagementFee"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionQuarterlyManagementFee" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionQuarterlyManagementFee" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionFixedDailyFee" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionFixedDailyFee" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionCommissionRate" xlink:label="RelatedPartyTransactionCommissionRate" xlink:title="RelatedPartyTransactionCommissionRate"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionCommissionRate" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionCommissionRate" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionCommissionRateOnEachVesselSaleAndPurchaseTransaction" xlink:label="RelatedPartyTransactionCommissionRateOnEachVesselSaleAndPurchaseTransaction" xlink:title="RelatedPartyTransactionCommissionRateOnEachVesselSaleAndPurchaseTransaction"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionCommissionRateOnEachVesselSaleAndPurchaseTransaction" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionCommissionRateOnEachVesselSaleAndPurchaseTransaction" order="5.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" order="6.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionManagementFees" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionManagementFees" order="7.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionCommissions" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionCommissions" order="8.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="RelatedPartyTransactionSaleAndPurchaseCommission" xlink:title="definition: RelatedPartyTransactionLineItems to RelatedPartyTransactionSaleAndPurchaseCommission" order="9.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="AccountsPayableRelatedPartiesCurrent" xlink:title="definition: RelatedPartyTransactionLineItems to AccountsPayableRelatedPartiesCurrent" order="10.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="11.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CastorShipsSAMember" xlink:label="CastorShipsSAMember" xlink:title="CastorShipsSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="RelatedPartyTransactionAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to RelatedPartyTransactionAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ManagementAgreementsMember" xlink:label="ManagementAgreementsMember" xlink:title="ManagementAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionDomain" xlink:to="ManagementAgreementsMember" xlink:title="definition: RelatedPartyTransactionDomain to ManagementAgreementsMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CommercialShipmanagementAgreementsMember" xlink:label="CommercialShipmanagementAgreementsMember" xlink:title="CommercialShipmanagementAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ManagementAgreementsMember" xlink:to="CommercialShipmanagementAgreementsMember" xlink:title="definition: ManagementAgreementsMember to CommercialShipmanagementAgreementsMember" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="IncomeStatementLocationAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to IncomeStatementLocationAxis" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ManagementFeesToRelatedPartyMember" xlink:label="ManagementFeesToRelatedPartyMember" xlink:title="ManagementFeesToRelatedPartyMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="IncomeStatementLocationDomain" xlink:to="ManagementFeesToRelatedPartyMember" xlink:title="definition: IncomeStatementLocationDomain to ManagementFeesToRelatedPartyMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VoyageExpensesMember" xlink:label="VoyageExpensesMember" xlink:title="VoyageExpensesMember"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/TransactionsWithRelatedPartiesVesselAcquisitionDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAdditions" xlink:label="PropertyPlantAndEquipmentAdditions" xlink:title="PropertyPlantAndEquipmentAdditions"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionLineItems" xlink:to="PropertyPlantAndEquipmentAdditions" xlink:title="definition: RelatedPartyTransactionLineItems to PropertyPlantAndEquipmentAdditions" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="RelatedPartyTransactionLineItems" xlink:to="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:title="definition: RelatedPartyTransactionLineItems to ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" order="3.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ThirdPartyInWhichFamilyMemberOfPetrosPanagiotidisHadMinorityInterestMember" xlink:label="ThirdPartyInWhichFamilyMemberOfPetrosPanagiotidisHadMinorityInterestMember" xlink:title="ThirdPartyInWhichFamilyMemberOfPetrosPanagiotidisHadMinorityInterestMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyDomain" xlink:to="ThirdPartyInWhichFamilyMemberOfPetrosPanagiotidisHadMinorityInterestMember" xlink:title="definition: RelatedPartyDomain to ThirdPartyInWhichFamilyMemberOfPetrosPanagiotidisHadMinorityInterestMember" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: ScheduleOfRelatedPartyTransactionsByRelatedPartyTable to PropertyPlantAndEquipmentByTypeAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicCallistoMember" xlink:label="MagicCallistoMember" xlink:title="MagicCallistoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicCallistoMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicCallistoMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/DeferredChargesNetDetails"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleNetBookValueDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="PropertyPlantAndEquipmentLineItems" xlink:title="PropertyPlantAndEquipmentLineItems"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MovementInPropertyPlantAndEquipmentRollForward" xlink:label="MovementInPropertyPlantAndEquipmentRollForward" xlink:title="MovementInPropertyPlantAndEquipmentRollForward"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="MovementInPropertyPlantAndEquipmentRollForward" xlink:title="definition: PropertyPlantAndEquipmentLineItems to MovementInPropertyPlantAndEquipmentRollForward" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MovementInAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipmentRollForward" xlink:label="MovementInAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipmentRollForward" xlink:title="MovementInAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipmentRollForward"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="MovementInAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipmentRollForward" xlink:title="definition: PropertyPlantAndEquipmentLineItems to MovementInAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipmentRollForward" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNetByTypeAbstract" xlink:label="PropertyPlantAndEquipmentNetByTypeAbstract" xlink:title="PropertyPlantAndEquipmentNetByTypeAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentNetByTypeAbstract" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentNetByTypeAbstract" order="3.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentNet" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentNet" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PropertyPlantAndEquipmentNetTransferToHeldForSale" xlink:label="PropertyPlantAndEquipmentNetTransferToHeldForSale" xlink:title="PropertyPlantAndEquipmentNetTransferToHeldForSale"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentNetTransferToHeldForSale" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentNetTransferToHeldForSale" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="definition: PropertyPlantAndEquipmentLineItems to AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationReclassificationsFromPropertyPlantAndEquipment1" xlink:label="AccumulatedDepreciationDepletionAndAmortizationReclassificationsFromPropertyPlantAndEquipment1" xlink:title="AccumulatedDepreciationDepletionAndAmortizationReclassificationsFromPropertyPlantAndEquipment1"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="AccumulatedDepreciationDepletionAndAmortizationReclassificationsFromPropertyPlantAndEquipment1" xlink:title="definition: PropertyPlantAndEquipmentLineItems to AccumulatedDepreciationDepletionAndAmortizationReclassificationsFromPropertyPlantAndEquipment1" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Depreciation" xlink:label="Depreciation" xlink:title="Depreciation"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="PropertyPlantAndEquipmentGross" xlink:title="PropertyPlantAndEquipmentGross"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentGross" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentGross" order="9.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentAdditions" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentAdditions" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTransfersAndChanges" xlink:label="PropertyPlantAndEquipmentTransfersAndChanges" xlink:title="PropertyPlantAndEquipmentTransfersAndChanges"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentTransfersAndChanges" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentTransfersAndChanges" order="11.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PropertyPlantAndEquipmentTransferToHeldForSale" xlink:label="PropertyPlantAndEquipmentTransferToHeldForSale" xlink:title="PropertyPlantAndEquipmentTransferToHeldForSale"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentTransferToHeldForSale" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentTransferToHeldForSale" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="ScheduleOfPropertyPlantAndEquipmentTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="definition: PropertyPlantAndEquipmentLineItems to ScheduleOfPropertyPlantAndEquipmentTable" order="13.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: ScheduleOfPropertyPlantAndEquipmentTable to PropertyPlantAndEquipmentByTypeAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselsMember" xlink:label="VesselsMember" xlink:title="VesselsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="VesselsMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to VesselsMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleVesselAcquisitionsAndOtherCapitalExpendituresDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNetAbstract" xlink:label="PropertyPlantAndEquipmentNetAbstract" xlink:title="PropertyPlantAndEquipmentNetAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentNetAbstract" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentNetAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsAcquired" xlink:label="NumberOfVesselsAcquired" xlink:title="NumberOfVesselsAcquired"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="NumberOfVesselsAcquired" xlink:title="definition: PropertyPlantAndEquipmentLineItems to NumberOfVesselsAcquired" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentAdditions" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentAdditions" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsMortgagedAsCollateral" xlink:label="NumberOfVesselsMortgagedAsCollateral" xlink:title="NumberOfVesselsMortgagedAsCollateral"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="NumberOfVesselsMortgagedAsCollateral" xlink:title="definition: PropertyPlantAndEquipmentLineItems to NumberOfVesselsMortgagedAsCollateral" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVessels" xlink:label="NumberOfVessels" xlink:title="NumberOfVessels"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="NumberOfVessels" xlink:title="definition: PropertyPlantAndEquipmentLineItems to NumberOfVessels" order="5.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentNet" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentNet" order="6.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="definition: PropertyPlantAndEquipmentLineItems to ScheduleOfPropertyPlantAndEquipmentTable" order="7.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MagicCallistoMember" xlink:label="MagicCallistoMember" xlink:title="MagicCallistoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="MagicCallistoMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to MagicCallistoMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VesselsMortgagedAsCollateralMember" xlink:label="VesselsMortgagedAsCollateralMember" xlink:title="VesselsMortgagedAsCollateralMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="VesselsMortgagedAsCollateralMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to VesselsMortgagedAsCollateralMember" order="2.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleAdvancesForVesselAcquisitionDetails"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselsNetAdvancesForVesselAcquisitionVesselHeldForSaleVesselHeldForSaleDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipmentAbstract" xlink:label="GainLossOnSaleOfPropertyPlantEquipmentAbstract" xlink:title="GainLossOnSaleOfPropertyPlantEquipmentAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="GainLossOnSaleOfPropertyPlantEquipmentAbstract" xlink:title="definition: PropertyPlantAndEquipmentLineItems to GainLossOnSaleOfPropertyPlantEquipmentAbstract" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentSalesPrice" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentSalesPrice" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf" xlink:label="ImpairmentOfLongLivedAssetsToBeDisposedOf" xlink:title="ImpairmentOfLongLivedAssetsToBeDisposedOf"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="ImpairmentOfLongLivedAssetsToBeDisposedOf" xlink:title="definition: PropertyPlantAndEquipmentLineItems to ImpairmentOfLongLivedAssetsToBeDisposedOf" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnDispositionOfAssets" xlink:label="GainLossOnDispositionOfAssets" xlink:title="GainLossOnDispositionOfAssets"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="GainLossOnDispositionOfAssets" xlink:title="definition: PropertyPlantAndEquipmentLineItems to GainLossOnDispositionOfAssets" order="4.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="definition: PropertyPlantAndEquipmentLineItems to ScheduleOfPropertyPlantAndEquipmentTable" order="5.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_WonderArcturusMember" xlink:label="WonderArcturusMember" xlink:title="WonderArcturusMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="WonderArcturusMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to WonderArcturusMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementScenarioAxis" xlink:label="StatementScenarioAxis" xlink:title="StatementScenarioAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="StatementScenarioAxis" xlink:title="definition: ScheduleOfPropertyPlantAndEquipmentTable to StatementScenarioAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="ScenarioUnspecifiedDomain" xlink:title="ScenarioUnspecifiedDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementScenarioAxis" xlink:to="ScenarioUnspecifiedDomain" xlink:title="definition: StatementScenarioAxis to ScenarioUnspecifiedDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementScenarioAxis" xlink:to="ScenarioUnspecifiedDomain_2" xlink:title="definition: StatementScenarioAxis to ScenarioUnspecifiedDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScenarioPlanMember" xlink:label="ScenarioPlanMember" xlink:title="ScenarioPlanMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ScenarioUnspecifiedDomain" xlink:to="ScenarioPlanMember" xlink:title="definition: ScenarioUnspecifiedDomain to ScenarioPlanMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebtLongtermDebtIncludingRelatedPartyDebtDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="DebtInstrumentLineItems" xlink:title="DebtInstrumentLineItems"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentsAbstract" xlink:label="DebtInstrumentsAbstract" xlink:title="DebtInstrumentsAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentsAbstract" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentsAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtByCurrentAndNoncurrentAbstract" xlink:label="LongTermDebtByCurrentAndNoncurrentAbstract" xlink:title="LongTermDebtByCurrentAndNoncurrentAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtByCurrentAndNoncurrentAbstract" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtByCurrentAndNoncurrentAbstract" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_LongTermDebtGrossCurrent" xlink:label="LongTermDebtGrossCurrent" xlink:title="LongTermDebtGrossCurrent"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtGrossCurrent" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtGrossCurrent" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsCurrentNet" xlink:label="DeferredFinanceCostsCurrentNet" xlink:title="DeferredFinanceCostsCurrentNet"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DeferredFinanceCostsCurrentNet" xlink:title="definition: DebtInstrumentLineItems to DeferredFinanceCostsCurrentNet" order="4.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="SecuredDebtCurrent" xlink:title="definition: DebtInstrumentLineItems to SecuredDebtCurrent" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_LongTermDebtGrossNoncurrent" xlink:label="LongTermDebtGrossNoncurrent" xlink:title="LongTermDebtGrossNoncurrent"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtGrossNoncurrent" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtGrossNoncurrent" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNoncurrentNet" xlink:label="DeferredFinanceCostsNoncurrentNet" xlink:title="DeferredFinanceCostsNoncurrentNet"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DeferredFinanceCostsNoncurrentNet" xlink:title="definition: DebtInstrumentLineItems to DeferredFinanceCostsNoncurrentNet" order="7.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="SecuredLongTermDebt" xlink:title="definition: DebtInstrumentLineItems to SecuredLongTermDebt" order="8.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentIssuer" xlink:label="DebtInstrumentIssuer" xlink:title="DebtInstrumentIssuer"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentIssuer" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentIssuer" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:label="DebtInstrumentCarryingAmount" xlink:title="DebtInstrumentCarryingAmount"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentCarryingAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentCarryingAmount" order="11.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNet" xlink:label="DeferredFinanceCostsNet" xlink:title="DeferredFinanceCostsNet"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DeferredFinanceCostsNet" xlink:title="definition: DebtInstrumentLineItems to DeferredFinanceCostsNet" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt" xlink:label="LongTermDebt" xlink:title="LongTermDebt"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:label="DebtInstrumentTable" xlink:title="DebtInstrumentTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="14.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtInstrumentTable" xlink:to="DebtInstrumentAxis" xlink:title="definition: DebtInstrumentTable to DebtInstrumentAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SeniorSecuredTeamLoanFacilityAlphaBankSA2019Member" xlink:label="SeniorSecuredTeamLoanFacilityAlphaBankSA2019Member" xlink:title="SeniorSecuredTeamLoanFacilityAlphaBankSA2019Member"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityAlphaBankSA2019Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityAlphaBankSA2019Member" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SeniorSecuredTeamLoanFacilityChaileaseInternationalInternationalFinancialServicesCoLtdMember" xlink:label="SeniorSecuredTeamLoanFacilityChaileaseInternationalInternationalFinancialServicesCoLtdMember" xlink:title="SeniorSecuredTeamLoanFacilityChaileaseInternationalInternationalFinancialServicesCoLtdMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityChaileaseInternationalInternationalFinancialServicesCoLtdMember" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityChaileaseInternationalInternationalFinancialServicesCoLtdMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" xlink:label="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" xlink:title="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" xlink:label="SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" xlink:title="SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" xlink:label="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" xlink:title="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SeniorSecuredTeamLoanFacilityChaileaseInternationalFinancialServicesSingaporePteLtdMember" xlink:label="SeniorSecuredTeamLoanFacilityChaileaseInternationalFinancialServicesSingaporePteLtdMember" xlink:title="SeniorSecuredTeamLoanFacilityChaileaseInternationalFinancialServicesSingaporePteLtdMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityChaileaseInternationalFinancialServicesSingaporePteLtdMember" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityChaileaseInternationalFinancialServicesSingaporePteLtdMember" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" xlink:label="SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" xlink:title="SeniorSecuredTeamLoanFacilityDeutscheBankAgMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" order="7.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebtLongtermDebtIncludingRelatedPartyDebtDetailsCalc2"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt110MillionTermLoanFacilityDetails">

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="3.0" t1:closed="true" t1:contextElement="segment"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt45MillionTermLoanFacilityDetails">

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="3.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityChaileaseInternationalInternationalFinancialServicesCoLtdMember" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityChaileaseInternationalInternationalFinancialServicesCoLtdMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt1529MillionTermLoanFacilityDetails">

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="3.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt180MillionTermLoanFacilityDetails">

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="3.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt4075MillionTermLoanFacilityDetails">

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="3.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt2315MillionTermLoanFacilityDetails">

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="3.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityChaileaseInternationalFinancialServicesSingaporePteLtdMember" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityChaileaseInternationalFinancialServicesSingaporePteLtdMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebt550MillionTermLoanFacilityDetails">

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfShipOwningSubsidiariesEnteringIntoTermLoanFacility" xlink:label="NumberOfShipOwningSubsidiariesEnteringIntoTermLoanFacility" xlink:title="NumberOfShipOwningSubsidiariesEnteringIntoTermLoanFacility"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="NumberOfShipOwningSubsidiariesEnteringIntoTermLoanFacility" xlink:title="definition: DebtInstrumentLineItems to NumberOfShipOwningSubsidiariesEnteringIntoTermLoanFacility" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DebtInstrumentNumberOfTranches" xlink:label="DebtInstrumentNumberOfTranches" xlink:title="DebtInstrumentNumberOfTranches"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentNumberOfTranches" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentNumberOfTranches" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTerm" xlink:label="DebtInstrumentTerm" xlink:title="DebtInstrumentTerm"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTerm" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTerm" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="DebtInstrumentBasisSpreadOnVariableRate1" xlink:title="DebtInstrumentBasisSpreadOnVariableRate1"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentBasisSpreadOnVariableRate1" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentBasisSpreadOnVariableRate1" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DebtInstrumentNumberOfPaymentInstallments" xlink:label="DebtInstrumentNumberOfPaymentInstallments" xlink:title="DebtInstrumentNumberOfPaymentInstallments"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentNumberOfPaymentInstallments" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentNumberOfPaymentInstallments" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFrequencyOfPeriodicPayment" xlink:label="DebtInstrumentFrequencyOfPeriodicPayment" xlink:title="DebtInstrumentFrequencyOfPeriodicPayment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFrequencyOfPeriodicPayment" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFrequencyOfPeriodicPayment" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentPeriodicPayment" xlink:label="DebtInstrumentPeriodicPayment" xlink:title="DebtInstrumentPeriodicPayment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentPeriodicPayment" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentPeriodicPayment" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid" xlink:label="DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid" xlink:title="DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DebtInstrumentTrailingPeriodToMaintainEbitdaToNetInterestExpenseRatio" xlink:label="DebtInstrumentTrailingPeriodToMaintainEbitdaToNetInterestExpenseRatio" xlink:title="DebtInstrumentTrailingPeriodToMaintainEbitdaToNetInterestExpenseRatio"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTrailingPeriodToMaintainEbitdaToNetInterestExpenseRatio" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTrailingPeriodToMaintainEbitdaToNetInterestExpenseRatio" order="11.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="12.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis" xlink:label="DebtInstrumentRedemptionPeriodAxis" xlink:title="DebtInstrumentRedemptionPeriodAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtInstrumentTable" xlink:to="DebtInstrumentRedemptionPeriodAxis" xlink:title="definition: DebtInstrumentTable to DebtInstrumentRedemptionPeriodAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain" xlink:label="DebtInstrumentRedemptionPeriodDomain" xlink:title="DebtInstrumentRedemptionPeriodDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="DebtInstrumentRedemptionPeriodAxis" xlink:to="DebtInstrumentRedemptionPeriodDomain" xlink:title="definition: DebtInstrumentRedemptionPeriodAxis to DebtInstrumentRedemptionPeriodDomain" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain" xlink:label="DebtInstrumentRedemptionPeriodDomain_2" xlink:title="DebtInstrumentRedemptionPeriodDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DebtInstrumentRedemptionPeriodAxis" xlink:to="DebtInstrumentRedemptionPeriodDomain_2" xlink:title="definition: DebtInstrumentRedemptionPeriodAxis to DebtInstrumentRedemptionPeriodDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember" xlink:label="DebtInstrumentRedemptionPeriodOneMember" xlink:title="DebtInstrumentRedemptionPeriodOneMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentRedemptionPeriodDomain" xlink:to="DebtInstrumentRedemptionPeriodOneMember" xlink:title="definition: DebtInstrumentRedemptionPeriodDomain to DebtInstrumentRedemptionPeriodOneMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember" xlink:label="DebtInstrumentRedemptionPeriodTwoMember" xlink:title="DebtInstrumentRedemptionPeriodTwoMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentRedemptionPeriodDomain" xlink:to="DebtInstrumentRedemptionPeriodTwoMember" xlink:title="definition: DebtInstrumentRedemptionPeriodDomain to DebtInstrumentRedemptionPeriodTwoMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentRedemptionPeriodThreeMember" xlink:label="DebtInstrumentRedemptionPeriodThreeMember" xlink:title="DebtInstrumentRedemptionPeriodThreeMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentRedemptionPeriodDomain" xlink:to="DebtInstrumentRedemptionPeriodThreeMember" xlink:title="definition: DebtInstrumentRedemptionPeriodDomain to DebtInstrumentRedemptionPeriodThreeMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis" xlink:label="VariableRateAxis" xlink:title="VariableRateAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="DebtInstrumentTable" xlink:to="VariableRateAxis" xlink:title="definition: DebtInstrumentTable to VariableRateAxis" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain" xlink:label="VariableRateDomain" xlink:title="VariableRateDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="VariableRateAxis" xlink:to="VariableRateDomain" xlink:title="definition: VariableRateAxis to VariableRateDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="VariableRateAxis" xlink:to="VariableRateDomain_2" xlink:title="definition: VariableRateAxis to VariableRateDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember" xlink:label="SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember" xlink:title="SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="VariableRateDomain" xlink:to="SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember" xlink:title="definition: VariableRateDomain to SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/LongtermDebtAnnualPrincipalPaymentsDetails">

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_MinimumLiquidityDeposits" xlink:label="MinimumLiquidityDeposits" xlink:title="MinimumLiquidityDeposits"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="MinimumLiquidityDeposits" xlink:title="definition: DebtInstrumentLineItems to MinimumLiquidityDeposits" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentFaceAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentFaceAmount" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DryDockingReserveAccounts" xlink:label="DryDockingReserveAccounts" xlink:title="DryDockingReserveAccounts"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DryDockingReserveAccounts" xlink:title="definition: DebtInstrumentLineItems to DryDockingReserveAccounts" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RetentionDeposits" xlink:label="RetentionDeposits" xlink:title="RetentionDeposits"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="RetentionDeposits" xlink:title="definition: DebtInstrumentLineItems to RetentionDeposits" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtByMaturityAbstract" xlink:label="LongTermDebtByMaturityAbstract" xlink:title="LongTermDebtByMaturityAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtByMaturityAbstract" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtByMaturityAbstract" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtWeightedAverageInterestRate" xlink:label="DebtWeightedAverageInterestRate" xlink:title="DebtWeightedAverageInterestRate"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtWeightedAverageInterestRate" xlink:title="definition: DebtInstrumentLineItems to DebtWeightedAverageInterestRate" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseLongTermDebt" xlink:label="InterestExpenseLongTermDebt" xlink:title="InterestExpenseLongTermDebt"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="InterestExpenseLongTermDebt" xlink:title="definition: DebtInstrumentLineItems to InterestExpenseLongTermDebt" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:label="LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:label="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:label="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" order="11.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:label="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:label="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:title="definition: DebtInstrumentLineItems to LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" order="13.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentCarryingAmount" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentCarryingAmount" order="14.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="DebtInstrumentLineItems" xlink:to="DebtInstrumentTable" xlink:title="definition: DebtInstrumentLineItems to DebtInstrumentTable" order="15.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityAlphaBankSA2021Member" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJanuary2021Member" order="3.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityHamburgCommercialBankAgJuly2021Member" order="4.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" xlink:title="definition: DebtInstrumentNameDomain to SeniorSecuredTeamLoanFacilityDeutscheBankAgMember" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ThirdPartyAndRelatedPartyDebtMember" xlink:label="ThirdPartyAndRelatedPartyDebtMember" xlink:title="ThirdPartyAndRelatedPartyDebtMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DebtInstrumentNameDomain" xlink:to="ThirdPartyAndRelatedPartyDebtMember" xlink:title="definition: DebtInstrumentNameDomain to ThirdPartyAndRelatedPartyDebtMember" order="6.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/EquityCapitalStructureCapitalStockDetails"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/EquityCapitalStructureAtthemarketCommonStockOfferingDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockLineItems" xlink:label="ClassOfStockLineItems" xlink:title="ClassOfStockLineItems"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockNumberOfSharesParValueAndOtherDisclosuresAbstract" xlink:label="CommonStockNumberOfSharesParValueAndOtherDisclosuresAbstract" xlink:title="CommonStockNumberOfSharesParValueAndOtherDisclosuresAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="CommonStockNumberOfSharesParValueAndOtherDisclosuresAbstract" xlink:title="definition: ClassOfStockLineItems to CommonStockNumberOfSharesParValueAndOtherDisclosuresAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CommonStockThatCanBeSoldValue" xlink:label="CommonStockThatCanBeSoldValue" xlink:title="CommonStockThatCanBeSoldValue"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="CommonStockThatCanBeSoldValue" xlink:title="definition: ClassOfStockLineItems to CommonStockThatCanBeSoldValue" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="StockIssuedDuringPeriodSharesNewIssues" xlink:title="StockIssuedDuringPeriodSharesNewIssues"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="StockIssuedDuringPeriodSharesNewIssues" xlink:title="definition: ClassOfStockLineItems to StockIssuedDuringPeriodSharesNewIssues" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:label="ProceedsFromIssuanceOrSaleOfEquity" xlink:title="ProceedsFromIssuanceOrSaleOfEquity"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="ProceedsFromIssuanceOrSaleOfEquity" xlink:title="definition: ClassOfStockLineItems to ProceedsFromIssuanceOrSaleOfEquity" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="SaleOfStockConsiderationReceivedOnTransaction"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockLineItems" xlink:to="SaleOfStockConsiderationReceivedOnTransaction" xlink:title="definition: ClassOfStockLineItems to SaleOfStockConsiderationReceivedOnTransaction" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="ScheduleOfStockByClassTable" xlink:title="ScheduleOfStockByClassTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ClassOfStockLineItems" xlink:to="ScheduleOfStockByClassTable" xlink:title="definition: ClassOfStockLineItems to ScheduleOfStockByClassTable" order="6.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="StatementEquityComponentsAxis" xlink:title="definition: ScheduleOfStockByClassTable to StatementEquityComponentsAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfStockByClassTable" xlink:to="RangeAxis" xlink:title="definition: ScheduleOfStockByClassTable to RangeAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="RangeMember_2" xlink:title="RangeMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember_2" xlink:title="definition: RangeAxis to RangeMember_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RangeMember" xlink:to="MaximumMember" xlink:title="definition: RangeMember to MaximumMember" order="1.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/EquityCapitalStructureReverseStockSplitDetails"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/CommitmentsAndContingenciesDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:label="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:title="PurchaseCommitmentExcludingLongtermCommitmentLineItems"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherCommitmentsAbstract" xlink:label="OtherCommitmentsAbstract" xlink:title="OtherCommitmentsAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="OtherCommitmentsAbstract" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to OtherCommitmentsAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsOnWhichBallastWaterManagementSystemsWereContractedToBeInstalled" xlink:label="NumberOfVesselsOnWhichBallastWaterManagementSystemsWereContractedToBeInstalled" xlink:title="NumberOfVesselsOnWhichBallastWaterManagementSystemsWereContractedToBeInstalled"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="NumberOfVesselsOnWhichBallastWaterManagementSystemsWereContractedToBeInstalled" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to NumberOfVesselsOnWhichBallastWaterManagementSystemsWereContractedToBeInstalled" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsOnWhichBallastWaterTreatmentSystemsWereCompletedAndPutIntoUse" xlink:label="NumberOfVesselsOnWhichBallastWaterTreatmentSystemsWereCompletedAndPutIntoUse" xlink:title="NumberOfVesselsOnWhichBallastWaterTreatmentSystemsWereCompletedAndPutIntoUse"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="NumberOfVesselsOnWhichBallastWaterTreatmentSystemsWereCompletedAndPutIntoUse" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to NumberOfVesselsOnWhichBallastWaterTreatmentSystemsWereCompletedAndPutIntoUse" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsOnWhichBallastWaterManagementSystemsWillBeInstalled" xlink:label="NumberOfVesselsOnWhichBallastWaterManagementSystemsWillBeInstalled" xlink:title="NumberOfVesselsOnWhichBallastWaterManagementSystemsWillBeInstalled"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="NumberOfVesselsOnWhichBallastWaterManagementSystemsWillBeInstalled" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to NumberOfVesselsOnWhichBallastWaterManagementSystemsWillBeInstalled" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfVesselsOnWhichBallastWaterManagementSystemsWereInProcessOfBeingInstalled" xlink:label="NumberOfVesselsOnWhichBallastWaterManagementSystemsWereInProcessOfBeingInstalled" xlink:title="NumberOfVesselsOnWhichBallastWaterManagementSystemsWereInProcessOfBeingInstalled"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="NumberOfVesselsOnWhichBallastWaterManagementSystemsWereInProcessOfBeingInstalled" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to NumberOfVesselsOnWhichBallastWaterManagementSystemsWereInProcessOfBeingInstalled" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfInstallationsExpectedToBeConcludedRemainderOfFiscalYear" xlink:label="NumberOfInstallationsExpectedToBeConcludedRemainderOfFiscalYear" xlink:title="NumberOfInstallationsExpectedToBeConcludedRemainderOfFiscalYear"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="NumberOfInstallationsExpectedToBeConcludedRemainderOfFiscalYear" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to NumberOfInstallationsExpectedToBeConcludedRemainderOfFiscalYear" order="6.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_NumberOfInstallationsExpectedToBeConcludedYearTwo" xlink:label="NumberOfInstallationsExpectedToBeConcludedYearTwo" xlink:title="NumberOfInstallationsExpectedToBeConcludedYearTwo"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="NumberOfInstallationsExpectedToBeConcludedYearTwo" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to NumberOfInstallationsExpectedToBeConcludedYearTwo" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PurchaseCommitmentRemainingMinimumAmountCommitted" xlink:label="PurchaseCommitmentRemainingMinimumAmountCommitted" xlink:title="PurchaseCommitmentRemainingMinimumAmountCommitted"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="PurchaseCommitmentRemainingMinimumAmountCommitted" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to PurchaseCommitmentRemainingMinimumAmountCommitted" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForeignCurrencyExchangeRateTranslation1" xlink:label="ForeignCurrencyExchangeRateTranslation1" xlink:title="ForeignCurrencyExchangeRateTranslation1"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="ForeignCurrencyExchangeRateTranslation1" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to ForeignCurrencyExchangeRateTranslation1" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear" xlink:label="PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear" xlink:title="PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear" order="10.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PurchaseObligationDueInNextTwelveMonths" xlink:label="PurchaseObligationDueInNextTwelveMonths" xlink:title="PurchaseObligationDueInNextTwelveMonths"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="PurchaseObligationDueInNextTwelveMonths" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to PurchaseObligationDueInNextTwelveMonths" order="11.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PurchaseObligationDueInSecondYear" xlink:label="PurchaseObligationDueInSecondYear" xlink:title="PurchaseObligationDueInSecondYear"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="PurchaseObligationDueInSecondYear" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to PurchaseObligationDueInSecondYear" order="12.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PurchaseCommitmentExcludingLongtermCommitmentTable" xlink:label="PurchaseCommitmentExcludingLongtermCommitmentTable" xlink:title="PurchaseCommitmentExcludingLongtermCommitmentTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="PurchaseCommitmentExcludingLongtermCommitmentLineItems" xlink:to="PurchaseCommitmentExcludingLongtermCommitmentTable" xlink:title="definition: PurchaseCommitmentExcludingLongtermCommitmentLineItems to PurchaseCommitmentExcludingLongtermCommitmentTable" order="13.0" t1:closed="true" t1:contextElement="segment"/>

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</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/EarningsPerShareDetails">

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<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ClassAWarrantMember" xlink:label="ClassAWarrantMember" xlink:title="ClassAWarrantMember"/>

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<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PrivatePlacementWarrantsMember" xlink:label="PrivatePlacementWarrantsMember" xlink:title="PrivatePlacementWarrantsMember"/>

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</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselRevenuesDetails">

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<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_TimeCharterContractTerm" xlink:label="TimeCharterContractTerm" xlink:title="TimeCharterContractTerm"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLeaseIncome" xlink:label="OperatingLeaseLeaseIncome" xlink:title="OperatingLeaseLeaseIncome"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="DisaggregationOfRevenueLineItems" xlink:to="OperatingLeaseLeaseIncome" xlink:title="definition: DisaggregationOfRevenueLineItems to OperatingLeaseLeaseIncome" order="3.0"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:label="IncreaseDecreaseInDeferredRevenue" xlink:title="IncreaseDecreaseInDeferredRevenue"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:label="ProductOrServiceAxis" xlink:title="ProductOrServiceAxis"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:label="ProductsAndServicesDomain" xlink:title="ProductsAndServicesDomain"/>

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<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VoyageCharterMember" xlink:label="VoyageCharterMember" xlink:title="VoyageCharterMember"/>

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<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PoolAgreementsMember" xlink:label="PoolAgreementsMember" xlink:title="PoolAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ProductsAndServicesDomain" xlink:to="PoolAgreementsMember" xlink:title="definition: ProductsAndServicesDomain to PoolAgreementsMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="MinimumMember" xlink:title="MinimumMember"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="MaximumMember" xlink:title="MaximumMember"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/VesselOperatingAndVoyageExpensesDetails"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/GeneralAndAdministrativeExpensesDetails"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/InterestAndFinanceCostsDetails"/>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SegmentInformationInformationAboutCompanySReportableSegmentsDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="SegmentReportingInformationLineItems" xlink:title="SegmentReportingInformationLineItems"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationProfitLossAbstract" xlink:label="SegmentReportingInformationProfitLossAbstract" xlink:title="SegmentReportingInformationProfitLossAbstract"/>

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<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VoyageExpenses" xlink:label="VoyageExpenses" xlink:title="VoyageExpenses"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="VoyageExpenses" xlink:title="definition: SegmentReportingInformationLineItems to VoyageExpenses" order="3.0"/>

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<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="RelatedPartyTransactionManagementFees" xlink:title="definition: SegmentReportingInformationLineItems to RelatedPartyTransactionManagementFees" order="5.0"/>

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<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="OperatingIncomeLoss" xlink:title="definition: SegmentReportingInformationLineItems to OperatingIncomeLoss" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpense" xlink:label="InterestExpense" xlink:title="InterestExpense"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="InterestExpense" xlink:title="definition: SegmentReportingInformationLineItems to InterestExpense" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="InvestmentIncomeInterest" xlink:title="InvestmentIncomeInterest"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingInformationLineItems" xlink:to="InvestmentIncomeInterest" xlink:title="definition: SegmentReportingInformationLineItems to InvestmentIncomeInterest" order="9.0"/>

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<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:title="ScheduleOfSegmentReportingInformationBySegmentTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SegmentReportingInformationLineItems" xlink:to="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:title="definition: SegmentReportingInformationLineItems to ScheduleOfSegmentReportingInformationBySegmentTable" order="13.0" t1:closed="true" t1:contextElement="segment"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsAxis" xlink:label="ConsolidationItemsAxis" xlink:title="ConsolidationItemsAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="ConsolidationItemsAxis" xlink:title="definition: ScheduleOfSegmentReportingInformationBySegmentTable to ConsolidationItemsAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain" xlink:label="ConsolidationItemsDomain" xlink:title="ConsolidationItemsDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ConsolidationItemsAxis" xlink:to="ConsolidationItemsDomain" xlink:title="definition: ConsolidationItemsAxis to ConsolidationItemsDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ConsolidationItemsAxis" xlink:to="ConsolidationItemsDomain_2" xlink:title="definition: ConsolidationItemsAxis to ConsolidationItemsDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingSegmentsMember" xlink:label="OperatingSegmentsMember" xlink:title="OperatingSegmentsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidationItemsDomain" xlink:to="OperatingSegmentsMember" xlink:title="definition: ConsolidationItemsDomain to OperatingSegmentsMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateNonSegmentMember" xlink:label="CorporateNonSegmentMember" xlink:title="CorporateNonSegmentMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidationItemsDomain" xlink:to="CorporateNonSegmentMember" xlink:title="definition: ConsolidationItemsDomain to CorporateNonSegmentMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="StatementBusinessSegmentsAxis" xlink:title="StatementBusinessSegmentsAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="StatementBusinessSegmentsAxis" xlink:title="definition: ScheduleOfSegmentReportingInformationBySegmentTable to StatementBusinessSegmentsAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain" xlink:label="SegmentDomain" xlink:title="SegmentDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="StatementBusinessSegmentsAxis" xlink:to="SegmentDomain" xlink:title="definition: StatementBusinessSegmentsAxis to SegmentDomain" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain" xlink:label="SegmentDomain_2" xlink:title="SegmentDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementBusinessSegmentsAxis" xlink:to="SegmentDomain_2" xlink:title="definition: StatementBusinessSegmentsAxis to SegmentDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DryBulkSegmentMember" xlink:label="DryBulkSegmentMember" xlink:title="DryBulkSegmentMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentDomain" xlink:to="DryBulkSegmentMember" xlink:title="definition: SegmentDomain to DryBulkSegmentMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_AframaxLr2TankerSegmentMember" xlink:label="AframaxLr2TankerSegmentMember" xlink:title="AframaxLr2TankerSegmentMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentDomain" xlink:to="AframaxLr2TankerSegmentMember" xlink:title="definition: SegmentDomain to AframaxLr2TankerSegmentMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_HandysizeTankerSegmentMember" xlink:label="HandysizeTankerSegmentMember" xlink:title="HandysizeTankerSegmentMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentDomain" xlink:to="HandysizeTankerSegmentMember" xlink:title="definition: SegmentDomain to HandysizeTankerSegmentMember" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:label="ProductOrServiceAxis" xlink:title="ProductOrServiceAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="ProductOrServiceAxis" xlink:title="definition: ScheduleOfSegmentReportingInformationBySegmentTable to ProductOrServiceAxis" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_TimeCharterMember" xlink:label="TimeCharterMember" xlink:title="TimeCharterMember"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_VoyageCharterMember" xlink:label="VoyageCharterMember" xlink:title="VoyageCharterMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ProductsAndServicesDomain" xlink:to="VoyageCharterMember" xlink:title="definition: ProductsAndServicesDomain to VoyageCharterMember" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PoolAgreementsMember" xlink:label="PoolAgreementsMember" xlink:title="PoolAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ProductsAndServicesDomain" xlink:to="PoolAgreementsMember" xlink:title="definition: ProductsAndServicesDomain to PoolAgreementsMember" order="3.0"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SegmentInformationReconciliationOfTotalSegmentAssetsToTotalAssetsDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingAssetReconcilingItemLineItems" xlink:label="SegmentReportingAssetReconcilingItemLineItems" xlink:title="SegmentReportingAssetReconcilingItemLineItems"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract" xlink:label="ReconciliationFromSegmentTotalsToConsolidatedAbstract" xlink:title="ReconciliationFromSegmentTotalsToConsolidatedAbstract"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingAssetReconcilingItemLineItems" xlink:to="ReconciliationFromSegmentTotalsToConsolidatedAbstract" xlink:title="definition: SegmentReportingAssetReconcilingItemLineItems to ReconciliationFromSegmentTotalsToConsolidatedAbstract" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets" xlink:label="Assets" xlink:title="Assets"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingAssetReconcilingItemLineItems" xlink:to="Assets" xlink:title="definition: SegmentReportingAssetReconcilingItemLineItems to Assets" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingAssetReconcilingItemLineItems" xlink:to="CashAndCashEquivalentsAtCarryingValue" xlink:title="definition: SegmentReportingAssetReconcilingItemLineItems to CashAndCashEquivalentsAtCarryingValue" order="3.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SegmentReportingAssetReconcilingItemLineItems" xlink:to="PrepaidExpenseAndOtherAssetsCurrent" xlink:title="definition: SegmentReportingAssetReconcilingItemLineItems to PrepaidExpenseAndOtherAssetsCurrent" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable" xlink:label="ReconciliationOfAssetsFromSegmentToConsolidatedTable" xlink:title="ReconciliationOfAssetsFromSegmentToConsolidatedTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SegmentReportingAssetReconcilingItemLineItems" xlink:to="ReconciliationOfAssetsFromSegmentToConsolidatedTable" xlink:title="definition: SegmentReportingAssetReconcilingItemLineItems to ReconciliationOfAssetsFromSegmentToConsolidatedTable" order="5.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ReconciliationOfAssetsFromSegmentToConsolidatedTable" xlink:to="ConsolidationItemsAxis" xlink:title="definition: ReconciliationOfAssetsFromSegmentToConsolidatedTable to ConsolidationItemsAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MaterialReconcilingItemsMember" xlink:label="MaterialReconcilingItemsMember" xlink:title="MaterialReconcilingItemsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ConsolidationItemsDomain" xlink:to="MaterialReconcilingItemsMember" xlink:title="definition: ConsolidationItemsDomain to MaterialReconcilingItemsMember" order="2.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ReconciliationOfAssetsFromSegmentToConsolidatedTable" xlink:to="StatementBusinessSegmentsAxis" xlink:title="definition: ReconciliationOfAssetsFromSegmentToConsolidatedTable to StatementBusinessSegmentsAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain" xlink:label="SegmentDomain" xlink:title="SegmentDomain"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain" xlink:label="SegmentDomain_2" xlink:title="SegmentDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DryBulkSegmentMember" xlink:label="DryBulkSegmentMember" xlink:title="DryBulkSegmentMember"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_AframaxLr2TankerSegmentMember" xlink:label="AframaxLr2TankerSegmentMember" xlink:title="AframaxLr2TankerSegmentMember"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_HandysizeTankerSegmentMember" xlink:label="HandysizeTankerSegmentMember" xlink:title="HandysizeTankerSegmentMember"/>

</link:definitionLink>

<link:definitionLink xlink:type="extended" xlink:role="http://castormaritime.com/role/SubsequentEventsDetails">

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventLineItems" xlink:label="SubsequentEventLineItems" xlink:title="SubsequentEventLineItems"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="GainLossOnSaleOfPropertyPlantEquipmentAbstract" xlink:title="definition: SubsequentEventLineItems to GainLossOnSaleOfPropertyPlantEquipmentAbstract" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionDueFromToRelatedPartyCurrentAbstract" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionDueFromToRelatedPartyCurrentAbstract" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionManagementRecoveryFeeMultiplier" xlink:label="RelatedPartyTransactionManagementRecoveryFeeMultiplier" xlink:title="RelatedPartyTransactionManagementRecoveryFeeMultiplier"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionManagementRecoveryFeeMultiplier" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionManagementRecoveryFeeMultiplier" order="3.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionQuarterlyManagementFee" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionQuarterlyManagementFee" order="4.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionCommissionRate" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionCommissionRate" order="5.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionCommissionRateOnEachVesselSaleAndPurchaseTransaction" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionCommissionRateOnEachVesselSaleAndPurchaseTransaction" order="6.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionFixedDailyFee" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionFixedDailyFee" order="7.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionTermOfAgreement" xlink:label="RelatedPartyTransactionTermOfAgreement" xlink:title="RelatedPartyTransactionTermOfAgreement"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionTermOfAgreement" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionTermOfAgreement" order="8.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionRenewalTermOfAgreement" xlink:label="RelatedPartyTransactionRenewalTermOfAgreement" xlink:title="RelatedPartyTransactionRenewalTermOfAgreement"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionRenewalTermOfAgreement" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionRenewalTermOfAgreement" order="9.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_RelatedPartyTransactionManagementTerminationFeeMultiplier" xlink:label="RelatedPartyTransactionManagementTerminationFeeMultiplier" xlink:title="RelatedPartyTransactionManagementTerminationFeeMultiplier"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="RelatedPartyTransactionManagementTerminationFeeMultiplier" xlink:title="definition: SubsequentEventLineItems to RelatedPartyTransactionManagementTerminationFeeMultiplier" order="10.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventLineItems" xlink:to="GainLossOnDispositionOfAssets" xlink:title="definition: SubsequentEventLineItems to GainLossOnDispositionOfAssets" order="11.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTable" xlink:label="SubsequentEventTable" xlink:title="SubsequentEventTable"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="SubsequentEventLineItems" xlink:to="SubsequentEventTable" xlink:title="definition: SubsequentEventLineItems to SubsequentEventTable" order="12.0" t1:closed="true" t1:contextElement="segment"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="StatementScenarioAxis" xlink:title="definition: SubsequentEventTable to StatementScenarioAxis" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="SubsequentEventTypeAxis" xlink:title="definition: SubsequentEventTable to SubsequentEventTypeAxis" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_2" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain_2" order="2.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember" xlink:label="SubsequentEventMember" xlink:title="SubsequentEventMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="SubsequentEventTypeDomain" xlink:to="SubsequentEventMember" xlink:title="definition: SubsequentEventTypeDomain to SubsequentEventMember" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="definition: SubsequentEventTable to RelatedPartyTransactionsByRelatedPartyAxis" order="3.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_CastorShipsSAMember" xlink:label="CastorShipsSAMember" xlink:title="CastorShipsSAMember"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_PavimarSAMember" xlink:label="PavimarSAMember" xlink:title="PavimarSAMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="RelatedPartyTransactionAxis" xlink:title="definition: SubsequentEventTable to RelatedPartyTransactionAxis" order="4.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_ManagementAgreementsMember" xlink:label="ManagementAgreementsMember" xlink:title="ManagementAgreementsMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="RelatedPartyTransactionDomain" xlink:to="ManagementAgreementsMember" xlink:title="definition: RelatedPartyTransactionDomain to ManagementAgreementsMember" order="1.0"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="SubsequentEventTable" xlink:to="PropertyPlantAndEquipmentByTypeAxis" xlink:title="definition: SubsequentEventTable to PropertyPlantAndEquipmentByTypeAxis" order="5.0"/>

<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_2" xlink:title="PropertyPlantAndEquipmentTypeDomain"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_DryBulkCarrierMember" xlink:label="DryBulkCarrierMember" xlink:title="DryBulkCarrierMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="DryBulkCarrierMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to DryBulkCarrierMember" order="1.0"/>

<link:loc xlink:type="locator" xlink:href="ctrm-20220630.xsd#ctrm_TankerMember" xlink:label="TankerMember" xlink:title="TankerMember"/>

<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="TankerMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to TankerMember" order="2.0"/>

</link:definitionLink>

</link:linkbase>

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Filing Submission 0001140361-22-028839 – Alternative Formats (Word / Rich Text, HTML, Plain Text, et al.)

Castor Maritime Inc. – ‘6-K’ for 6/30/22 – ‘EX-101.DEF’

On: Tuesday, 8/9/22, at 9:16am ET · For: 6/30/22 · Accession #: 1140361-22-28839 · File #: 1-38802

Previous ‘6-K’: ‘6-K’ on / for 8/9/22 · Next: ‘6-K’ on / for 11/8/22 · Latest: ‘6-K’ on / for 4/22/24

Current, Quarterly or Annual Report by a Foreign Issuer — Form 6-K — SEA’34Filing Table of Contents

‘EX-101.DEF’ — XBRL Definitions — ctrm-20220630_def

This Exhibit is an XBRL XML File.

Current, Quarterly or Annual Report by a Foreign Issuer — Form 6-K — SEA’34

Filing Table of Contents