<?xml version="1.0" encoding="us-ascii"?>
<!-- XBRL document created with Praxa -->
<!-- Copyright (c) 2026 Praxa LLC. All Rights Reserved.-->
<!-- Creation Date: 2026-08-12T19:21:21.7275+00:00 -->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/SupplementalCashFlowInformationScheduleofReconciliationoftheLiabilitiesArisingfromFinancingActivitiesDetails" xlink:href="tsat-20260630.xsd#SupplementalCashFlowInformationScheduleofReconciliationoftheLiabilitiesArisingfromFinancingActivitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetails" xlink:href="tsat-20260630.xsd#CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/CommitmentsandContingentLiabilitiesDetails" xlink:href="tsat-20260630.xsd#CommitmentsandContingentLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/UnauditedInterimCondensedConsolidatedStatementsofChangesinShareholdersEquity" xlink:href="tsat-20260630.xsd#UnauditedInterimCondensedConsolidatedStatementsofChangesinShareholdersEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareCapitalTables" xlink:href="tsat-20260630.xsd#ShareCapitalTables" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/SegmentInformationDetails" xlink:href="tsat-20260630.xsd#SegmentInformationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/BasisofPresentationandGoingConcernDetails" xlink:href="tsat-20260630.xsd#BasisofPresentationandGoingConcernDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetails" xlink:href="tsat-20260630.xsd#FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareCapitalDetails" xlink:href="tsat-20260630.xsd#ShareCapitalDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetails" xlink:href="tsat-20260630.xsd#FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetails" xlink:href="tsat-20260630.xsd#ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/SegmentInformationScheduleofEquipmentSalesDetails" xlink:href="tsat-20260630.xsd#SegmentInformationScheduleofEquipmentSalesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/SegmentInformationScheduleofGeographicRegionsDetails" xlink:href="tsat-20260630.xsd#SegmentInformationScheduleofGeographicRegionsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails3" xlink:href="tsat-20260630.xsd#ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails3" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetails" xlink:href="tsat-20260630.xsd#ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/GoodwillandIntangibleAssetsDetails" xlink:href="tsat-20260630.xsd#GoodwillandIntangibleAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/IndebtednessDetails" xlink:href="tsat-20260630.xsd#IndebtednessDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetails" xlink:href="tsat-20260630.xsd#SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/LeaseLiabilitiesScheduleofExpectedUndiscountedContractualCashFlowsoftheLeaseLiabilitiesDetails" xlink:href="tsat-20260630.xsd#LeaseLiabilitiesScheduleofExpectedUndiscountedContractualCashFlowsoftheLeaseLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/IndebtednessScheduleofIndebtednessDetails" xlink:href="tsat-20260630.xsd#IndebtednessScheduleofIndebtednessDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareBasedCompensationPlansDetails" xlink:href="tsat-20260630.xsd#ShareBasedCompensationPlansDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/EarningsPerShareScheduleofReconciliationsoftheDenominatorsoftheBasicandDilutedPerShareDetails" xlink:href="tsat-20260630.xsd#EarningsPerShareScheduleofReconciliationsoftheDenominatorsoftheBasicandDilutedPerShareDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/FinancialInstrumentsDetails" xlink:href="tsat-20260630.xsd#FinancialInstrumentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofPercentageofFaceValueoftheIndebtednessDetails" xlink:href="tsat-20260630.xsd#FinancialInstrumentsScheduleofPercentageofFaceValueoftheIndebtednessDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/EmployeeBenefitPlansScheduleofExpensesIncludedontheCondensedConsolidatedStatementsofIncomeLossDetails" xlink:href="tsat-20260630.xsd#EmployeeBenefitPlansScheduleofExpensesIncludedontheCondensedConsolidatedStatementsofIncomeLossDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetails" xlink:href="tsat-20260630.xsd#FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/IndebtednessScheduleofIndebtednessParentheticalsDetails" xlink:href="tsat-20260630.xsd#IndebtednessScheduleofIndebtednessParentheticalsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/IndebtednessScheduleofActivityinDeferredFinancingChargesDetails" xlink:href="tsat-20260630.xsd#IndebtednessScheduleofActivityinDeferredFinancingChargesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/NonControllingInterestDetails" xlink:href="tsat-20260630.xsd#NonControllingInterestDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails1" xlink:href="tsat-20260630.xsd#ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails1" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails2" xlink:href="tsat-20260630.xsd#ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails2" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/GovernmentGrantDetails" xlink:href="tsat-20260630.xsd#GovernmentGrantDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/EmployeeBenefitPlansScheduleofBalanceSheetObligationsDistributedBetweenPensionandOtherPostEmploymentBenefitsDetails" xlink:href="tsat-20260630.xsd#EmployeeBenefitPlansScheduleofBalanceSheetObligationsDistributedBetweenPensionandOtherPostEmploymentBenefitsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofValueoftheTelesatFinancingWarrantsDetails" xlink:href="tsat-20260630.xsd#FinancialInstrumentsScheduleofValueoftheTelesatFinancingWarrantsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/EventsAftertheReportingPeriodDetails" xlink:href="tsat-20260630.xsd#EventsAftertheReportingPeriodDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofInterestPayableandInterestPaymentsDetails" xlink:href="tsat-20260630.xsd#FinancialInstrumentsScheduleofInterestPayableandInterestPaymentsDetails" xlink:type="simple" />
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/SupplementalCashFlowInformationScheduleofReconciliationoftheLiabilitiesArisingfromFinancingActivitiesDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessMember" xlink:label="tsat_IndebtednessMember_1672" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SatellitePerformanceIncentivePaymentsMember" xlink:label="tsat_SatellitePerformanceIncentivePaymentsMember_1673" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LeaseLiabilitiesMember" xlink:label="ifrs-full_LeaseLiabilitiesMember_1674" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ForeignExchange" xlink:label="tsat_ForeignExchange_1685" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GainOnRepurchaseOfDebt" xlink:label="tsat_GainOnRepurchaseOfDebt_1941" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_InflowsOfCashFromFinancingActivities" xlink:label="tsat_InflowsOfCashFromFinancingActivities_1677" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_InterestAccrued" xlink:label="tsat_InterestAccrued_1681" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NoncashAdditions" xlink:label="tsat_NoncashAdditions_1683" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NoncashTransferFromDeferredChargesToIndebtednessOfDebtIssueCostsAndWarrants" xlink:label="tsat_NoncashTransferFromDeferredChargesToIndebtednessOfDebtIssueCostsAndWarrants_1682" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NoncashTransfersFromFinancingActivities" xlink:label="tsat_NoncashTransfersFromFinancingActivities_1684" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OutflowsOfCashFromFinancingActivities" xlink:label="tsat_OutflowsOfCashFromFinancingActivities_1678" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems" xlink:label="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SupplementalCashFlowInformationScheduleofReconciliationoftheLiabilitiesarisingfromFinancingActivitiesDetailsTable" xlink:label="tsat_SupplementalCashFlowInformationScheduleofReconciliationoftheLiabilitiesarisingfromFinancingActivitiesDetailsTable_1670" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1671" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1910" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestPaidClassifiedAsFinancingActivities" xlink:label="ifrs-full_InterestPaidClassifiedAsFinancingActivities_1680" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LongtermBorrowings" xlink:label="ifrs-full_LongtermBorrowings_1686" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_AmortisationOfDeferredFinancingCostsPrepaymentOptionsAndLossOnRepayment" xlink:label="tsat_AmortisationOfDeferredFinancingCostsPrepaymentOptionsAndLossOnRepayment_1679" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1910_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1910" xlink:to="tsat_IndebtednessMember_1672" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1910" xlink:to="tsat_SatellitePerformanceIncentivePaymentsMember_1673" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1910" xlink:to="ifrs-full_LeaseLiabilitiesMember_1674" />
    <link:definitionArc xlink:type="arc" order="21.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_ForeignExchange_1685" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_GainOnRepurchaseOfDebt_1941" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_InflowsOfCashFromFinancingActivities_1677" />
    <link:definitionArc xlink:type="arc" order="19.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_InterestAccrued_1681" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_NoncashAdditions_1683" />
    <link:definitionArc xlink:type="arc" order="20.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_NoncashTransferFromDeferredChargesToIndebtednessOfDebtIssueCostsAndWarrants_1682" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_NoncashTransfersFromFinancingActivities_1684" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_OutflowsOfCashFromFinancingActivities_1678" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_SupplementalCashFlowInformationScheduleofReconciliationoftheLiabilitiesarisingfromFinancingActivitiesDetailsTable_1670" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_SupplementalCashFlowInformationScheduleofReconciliationoftheLiabilitiesarisingfromFinancingActivitiesDetailsTable_1670" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1671" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1671" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1910" />
    <link:definitionArc xlink:type="arc" order="18.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="ifrs-full_InterestPaidClassifiedAsFinancingActivities_1680" />
    <link:definitionArc xlink:type="arc" order="22.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="ifrs-full_LongtermBorrowings_1686" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfReconciliationOfTheLiabilitiesArisingFromFinancingActivitiesLineItems_1675" xlink:to="tsat_AmortisationOfDeferredFinancingCostsPrepaymentOptionsAndLossOnRepayment_1679" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1671" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1910_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember" xlink:label="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1707" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanFourYearsAndNotLaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanFourYearsAndNotLaterThanFiveYearsMember_1708" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanFiveYearsMember_1709" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PropertyLeasesMember" xlink:label="tsat_PropertyLeasesMember_1712" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotLaterThanOneYearMember" xlink:label="ifrs-full_NotLaterThanOneYearMember_1704" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember" xlink:label="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1705" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember" xlink:label="ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember_1706" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CapitalCommitmentsMember" xlink:label="tsat_CapitalCommitmentsMember_1713" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherOperatingCommitmentsMember" xlink:label="tsat_OtherOperatingCommitmentsMember_1714" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusAxis" xlink:label="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusAxis_1710" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain" xlink:label="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain_1711" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetailsTable" xlink:label="tsat_CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetailsTable_1701" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityAxis" xlink:label="ifrs-full_MaturityAxis_1702" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1703" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ContractualObligationsLineItems" xlink:label="tsat_ContractualObligationsLineItems_1715" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ContractualCapitalCommitments" xlink:label="ifrs-full_ContractualCapitalCommitments_1716" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain" xlink:label="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain_1711_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1703_default" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1703" xlink:to="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1707" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1703" xlink:to="ifrs-full_LaterThanFourYearsAndNotLaterThanFiveYearsMember_1708" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1703" xlink:to="ifrs-full_LaterThanFiveYearsMember_1709" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain_1711" xlink:to="tsat_PropertyLeasesMember_1712" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1703" xlink:to="ifrs-full_NotLaterThanOneYearMember_1704" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1703" xlink:to="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1705" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1703" xlink:to="ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember_1706" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain_1711" xlink:to="tsat_CapitalCommitmentsMember_1713" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain_1711" xlink:to="tsat_OtherOperatingCommitmentsMember_1714" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetailsTable_1701" xlink:to="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusAxis_1710" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusAxis_1710" xlink:to="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain_1711" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_ContractualObligationsLineItems_1715" xlink:to="tsat_CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetailsTable_1701" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_CommitmentsandContingentLiabilitiesScheduleofOffBalanceSheetContractualObligationsDetailsTable_1701" xlink:to="ifrs-full_MaturityAxis_1702" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_MaturityAxis_1702" xlink:to="ifrs-full_MaturityDomain_1703" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ContractualObligationsLineItems_1715" xlink:to="ifrs-full_ContractualCapitalCommitments_1716" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusAxis_1710" xlink:to="ifrs-full_PropertyPlantAndEquipmentByOperatingLeaseStatusDomain_1711_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_MaturityAxis_1702" xlink:to="ifrs-full_MaturityDomain_1703_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/CommitmentsandContingentLiabilitiesDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PSPMember" xlink:label="tsat_PSPMember_1877" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CommitmentsandContingentLiabilitiesDetailsTable" xlink:label="tsat_CommitmentsandContingentLiabilitiesDetailsTable_1874" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfRelatedPartiesAxis" xlink:label="ifrs-full_CategoriesOfRelatedPartiesAxis_1875" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfRelatedPartiesDomain" xlink:label="ifrs-full_CategoriesOfRelatedPartiesDomain_1876" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CommitmentsAndContingentLiabilitiesLineItems" xlink:label="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DefinedBenefitObligationAtPresentValue" xlink:label="ifrs-full_DefinedBenefitObligationAtPresentValue_1879" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Prepayments" xlink:label="ifrs-full_Prepayments_1880" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncomeFromFinesAndPenalties" xlink:label="ifrs-full_IncomeFromFinesAndPenalties_1881" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_InterestAndPenalties" xlink:label="tsat_InterestAndPenalties_1882" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ResearchAndDevelopmentExpense" xlink:label="ifrs-full_ResearchAndDevelopmentExpense_1931" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OutstandingPercentage" xlink:label="tsat_OutstandingPercentage_1932" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfRelatedPartiesDomain" xlink:label="ifrs-full_CategoriesOfRelatedPartiesDomain_1876_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_CategoriesOfRelatedPartiesDomain_1876" xlink:to="tsat_PSPMember_1877" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" xlink:to="tsat_CommitmentsandContingentLiabilitiesDetailsTable_1874" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_CommitmentsandContingentLiabilitiesDetailsTable_1874" xlink:to="ifrs-full_CategoriesOfRelatedPartiesAxis_1875" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_CategoriesOfRelatedPartiesAxis_1875" xlink:to="ifrs-full_CategoriesOfRelatedPartiesDomain_1876" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" xlink:to="ifrs-full_DefinedBenefitObligationAtPresentValue_1879" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" xlink:to="ifrs-full_Prepayments_1880" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" xlink:to="ifrs-full_IncomeFromFinesAndPenalties_1881" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" xlink:to="tsat_InterestAndPenalties_1882" />
    <link:definitionArc xlink:type="arc" order="36.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" xlink:to="ifrs-full_ResearchAndDevelopmentExpense_1931" />
    <link:definitionArc xlink:type="arc" order="37.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_CommitmentsAndContingentLiabilitiesLineItems_1878" xlink:to="tsat_OutstandingPercentage_1932" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_CategoriesOfRelatedPartiesAxis_1875" xlink:to="ifrs-full_CategoriesOfRelatedPartiesDomain_1876_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/UnauditedInterimCondensedConsolidatedStatementsofChangesinShareholdersEquity" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ParentMember" xlink:label="ifrs-full_ParentMember_1046" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NoncontrollingInterestsMember" xlink:label="ifrs-full_NoncontrollingInterestsMember_1047" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OrdinarySharesMember" xlink:label="ifrs-full_OrdinarySharesMember_1041" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RetainedEarningsMember" xlink:label="ifrs-full_RetainedEarningsMember_1042" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ReserveOfRemeasurementsOfDefinedBenefitPlansMember" xlink:label="ifrs-full_ReserveOfRemeasurementsOfDefinedBenefitPlansMember_1043" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ReserveOfExchangeDifferencesOnTranslationMember" xlink:label="ifrs-full_ReserveOfExchangeDifferencesOnTranslationMember_1044" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherReservesMember" xlink:label="ifrs-full_OtherReservesMember_1045" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_StatementOfChangesInEquityTable" xlink:label="ifrs-full_StatementOfChangesInEquityTable_1039" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain" xlink:label="ifrs-full_ComponentsOfEquityDomain_1048" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_StatementOfChangesInEquityLineItems" xlink:label="ifrs-full_StatementOfChangesInEquityLineItems_1049" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Equity" xlink:label="ifrs-full_Equity_1050" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfitLoss" xlink:label="ifrs-full_ProfitLoss_1051" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssueOfEquity" xlink:label="ifrs-full_IssueOfEquity_1052" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityAxis" xlink:label="ifrs-full_ComponentsOfEquityAxis_1040" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_StockIssuedDuringPeriodValueOfExchangeOfLimitedPartnershipUnitsForPublicShares" xlink:label="tsat_StockIssuedDuringPeriodValueOfExchangeOfLimitedPartnershipUnitsForPublicShares_1053" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherComprehensiveIncome" xlink:label="ifrs-full_OtherComprehensiveIncome_1054" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncreaseDecreaseThroughSharebasedPaymentTransactions" xlink:label="ifrs-full_IncreaseDecreaseThroughSharebasedPaymentTransactions_1055" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain" xlink:label="ifrs-full_ComponentsOfEquityDomain_1048_default" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1048" xlink:to="ifrs-full_ParentMember_1046" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1048" xlink:to="ifrs-full_NoncontrollingInterestsMember_1047" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1048" xlink:to="ifrs-full_OrdinarySharesMember_1041" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1048" xlink:to="ifrs-full_RetainedEarningsMember_1042" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1048" xlink:to="ifrs-full_ReserveOfRemeasurementsOfDefinedBenefitPlansMember_1043" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1048" xlink:to="ifrs-full_ReserveOfExchangeDifferencesOnTranslationMember_1044" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1048" xlink:to="ifrs-full_OtherReservesMember_1045" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_StatementOfChangesInEquityLineItems_1049" xlink:to="ifrs-full_StatementOfChangesInEquityTable_1039" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ComponentsOfEquityAxis_1040" xlink:to="ifrs-full_ComponentsOfEquityDomain_1048" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_StatementOfChangesInEquityLineItems_1049" xlink:to="ifrs-full_Equity_1050" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_StatementOfChangesInEquityLineItems_1049" xlink:to="ifrs-full_ProfitLoss_1051" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_StatementOfChangesInEquityLineItems_1049" xlink:to="ifrs-full_IssueOfEquity_1052" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ifrs-full_StatementOfChangesInEquityTable_1039" xlink:to="ifrs-full_ComponentsOfEquityAxis_1040" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_StatementOfChangesInEquityLineItems_1049" xlink:to="tsat_StockIssuedDuringPeriodValueOfExchangeOfLimitedPartnershipUnitsForPublicShares_1053" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_StatementOfChangesInEquityLineItems_1049" xlink:to="ifrs-full_OtherComprehensiveIncome_1054" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_StatementOfChangesInEquityLineItems_1049" xlink:to="ifrs-full_IncreaseDecreaseThroughSharebasedPaymentTransactions_1055" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ComponentsOfEquityAxis_1040" xlink:to="ifrs-full_ComponentsOfEquityDomain_1048_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareCapitalTables" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatPublicSharesMember" xlink:label="tsat_TelesatPublicSharesMember_1239" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LimitedPartnershipUnitsMember" xlink:label="tsat_LimitedPartnershipUnitsMember_1240" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareCapitalTablesTable" xlink:label="tsat_ShareCapitalTablesTable_1236" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis_1237" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_1238" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfClassesOfShareCapitalLineItems" xlink:label="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1241" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ScheduleOfNumberOfSharesAndStatedValueOfOutstandingShares" xlink:label="tsat_ScheduleOfNumberOfSharesAndStatedValueOfOutstandingShares_1242" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_1238_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain_1238" xlink:to="tsat_TelesatPublicSharesMember_1239" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain_1238" xlink:to="tsat_LimitedPartnershipUnitsMember_1240" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1241" xlink:to="tsat_ShareCapitalTablesTable_1236" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareCapitalTablesTable_1236" xlink:to="srt_CounterpartyNameAxis_1237" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_CounterpartyNameAxis_1237" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_1238" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1241" xlink:to="tsat_ScheduleOfNumberOfSharesAndStatedValueOfOutstandingShares_1242" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_CounterpartyNameAxis_1237" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_1238_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GEOMember" xlink:label="tsat_GEOMember_1282" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherMember" xlink:label="tsat_OtherMember_1283" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LEOMember" xlink:label="tsat_LEOMember_1284" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BroadcastMember" xlink:label="tsat_BroadcastMember_1287" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_EnterpriseMember" xlink:label="tsat_EnterpriseMember_1288" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ConsultingAndOtherMember" xlink:label="tsat_ConsultingAndOtherMember_1289" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestExpense" xlink:label="ifrs-full_InterestExpense_1300" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainsLossesOnChangeInFairValueOfDerivatives" xlink:label="ifrs-full_GainsLossesOnChangeInFairValueOfDerivatives_1301" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestRevenueExpense" xlink:label="ifrs-full_InterestRevenueExpense_1302" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GainsLossesOnExchangeDifferencesOnTranslationBeforeTax" xlink:label="ifrs-full_GainsLossesOnExchangeDifferencesOnTranslationBeforeTax_1303" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfitLossBeforeTax" xlink:label="ifrs-full_ProfitLossBeforeTax_1304" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IncomeTaxExpenseContinuingOperations" xlink:label="ifrs-full_IncomeTaxExpenseContinuingOperations_1305" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems" xlink:label="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ExpenseFromSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets" xlink:label="ifrs-full_ExpenseFromSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets_1294" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DepreciationExpense" xlink:label="ifrs-full_DepreciationExpense_1296" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AmortisationExpense" xlink:label="ifrs-full_AmortisationExpense_1297" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherGainsLosses" xlink:label="ifrs-full_OtherGainsLosses_1298" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProfitLoss" xlink:label="ifrs-full_ProfitLoss_1306" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NonrecurringItems" xlink:label="tsat_NonrecurringItems_1295" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RevenueAndOperatingIncome" xlink:label="ifrs-full_RevenueAndOperatingIncome_1299" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CapitalExpenditures" xlink:label="tsat_CapitalExpenditures_1307" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GainOnRepurchaseOfDebt" xlink:label="tsat_GainOnRepurchaseOfDebt_1933" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProductsAndServicesAxis" xlink:label="ifrs-full_ProductsAndServicesAxis_1285" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProductsAndServicesDomain" xlink:label="ifrs-full_ProductsAndServicesDomain_1286" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetailsTable" xlink:label="tsat_SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetailsTable_1279" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SegmentsAxis" xlink:label="ifrs-full_SegmentsAxis_1280" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SegmentsDomain" xlink:label="ifrs-full_SegmentsDomain_1281" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Revenue" xlink:label="ifrs-full_Revenue_1291" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OperatingExpensesNetOfSharebasedCompensationAndNonrecurringItems" xlink:label="tsat_OperatingExpensesNetOfSharebasedCompensationAndNonrecurringItems_1292" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_AdjustedEarningsBeforeInterestTaxesDepreciationandAmortization" xlink:label="tsat_AdjustedEarningsBeforeInterestTaxesDepreciationandAmortization_1293" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProductsAndServicesDomain" xlink:label="ifrs-full_ProductsAndServicesDomain_1286_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SegmentsDomain" xlink:label="ifrs-full_SegmentsDomain_1281_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_SegmentsDomain_1281" xlink:to="tsat_GEOMember_1282" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_SegmentsDomain_1281" xlink:to="tsat_OtherMember_1283" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_SegmentsDomain_1281" xlink:to="tsat_LEOMember_1284" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ProductsAndServicesDomain_1286" xlink:to="tsat_BroadcastMember_1287" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ProductsAndServicesDomain_1286" xlink:to="tsat_EnterpriseMember_1288" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ProductsAndServicesDomain_1286" xlink:to="tsat_ConsultingAndOtherMember_1289" />
    <link:definitionArc xlink:type="arc" order="20.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_InterestExpense_1300" />
    <link:definitionArc xlink:type="arc" order="21.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_GainsLossesOnChangeInFairValueOfDerivatives_1301" />
    <link:definitionArc xlink:type="arc" order="22.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_InterestRevenueExpense_1302" />
    <link:definitionArc xlink:type="arc" order="24.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_GainsLossesOnExchangeDifferencesOnTranslationBeforeTax_1303" />
    <link:definitionArc xlink:type="arc" order="25.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_ProfitLossBeforeTax_1304" />
    <link:definitionArc xlink:type="arc" order="26.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_IncomeTaxExpenseContinuingOperations_1305" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_ExpenseFromSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets_1294" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_DepreciationExpense_1296" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_AmortisationExpense_1297" />
    <link:definitionArc xlink:type="arc" order="18.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_OtherGainsLosses_1298" />
    <link:definitionArc xlink:type="arc" order="27.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_ProfitLoss_1306" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="tsat_NonrecurringItems_1295" />
    <link:definitionArc xlink:type="arc" order="19.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_RevenueAndOperatingIncome_1299" />
    <link:definitionArc xlink:type="arc" order="28.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="tsat_CapitalExpenditures_1307" />
    <link:definitionArc xlink:type="arc" order="23.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="tsat_GainOnRepurchaseOfDebt_1933" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetailsTable_1279" xlink:to="ifrs-full_ProductsAndServicesAxis_1285" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ProductsAndServicesAxis_1285" xlink:to="ifrs-full_ProductsAndServicesDomain_1286" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="tsat_SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetailsTable_1279" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_SegmentInformationScheduleofCODMandtheReconciliationThereoftotheNetIncomeLossDetailsTable_1279" xlink:to="ifrs-full_SegmentsAxis_1280" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_SegmentsAxis_1280" xlink:to="ifrs-full_SegmentsDomain_1281" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="ifrs-full_Revenue_1291" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="tsat_OperatingExpensesNetOfSharebasedCompensationAndNonrecurringItems_1292" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1290" xlink:to="tsat_AdjustedEarningsBeforeInterestTaxesDepreciationandAmortization_1293" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ProductsAndServicesAxis_1285" xlink:to="ifrs-full_ProductsAndServicesDomain_1286_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_SegmentsAxis_1280" xlink:to="ifrs-full_SegmentsDomain_1281_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/BasisofPresentationandGoingConcernDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ForecastMember" xlink:label="tsat_ForecastMember_1962" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatGEOMember" xlink:label="tsat_TelesatGEOMember_1722" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BasisofPresentationandGoingConcernDetailsTable" xlink:label="tsat_BasisofPresentationandGoingConcernDetailsTable_1719" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodDomain" xlink:label="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1961" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LiquidityAxis" xlink:label="tsat_LiquidityAxis_1720" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LiquidityDomainDomain" xlink:label="tsat_LiquidityDomainDomain_1721" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BasisOfPresentationAndGoingConcernLineItems" xlink:label="tsat_BasisOfPresentationAndGoingConcernLineItems_1723" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CurrentLiabilities" xlink:label="ifrs-full_CurrentLiabilities_1724" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CashAndCashEquivalents" xlink:label="ifrs-full_CashAndCashEquivalents_1725" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinanceProvidedForFurtherSourceOfLiquidity" xlink:label="tsat_FinanceProvidedForFurtherSourceOfLiquidity_1959" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodAxis" xlink:label="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1960" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodDomain" xlink:label="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1961_default" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LiquidityDomainDomain" xlink:label="tsat_LiquidityDomainDomain_1721_default" />
    <link:definitionArc xlink:type="arc" order="52.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1961" xlink:to="tsat_ForecastMember_1962" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_LiquidityDomainDomain_1721" xlink:to="tsat_TelesatGEOMember_1722" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_BasisOfPresentationAndGoingConcernLineItems_1723" xlink:to="tsat_BasisofPresentationandGoingConcernDetailsTable_1719" />
    <link:definitionArc xlink:type="arc" order="51.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1960" xlink:to="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1961" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_BasisofPresentationandGoingConcernDetailsTable_1719" xlink:to="tsat_LiquidityAxis_1720" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="tsat_LiquidityAxis_1720" xlink:to="tsat_LiquidityDomainDomain_1721" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_BasisOfPresentationAndGoingConcernLineItems_1723" xlink:to="ifrs-full_CurrentLiabilities_1724" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_BasisOfPresentationAndGoingConcernLineItems_1723" xlink:to="ifrs-full_CashAndCashEquivalents_1725" />
    <link:definitionArc xlink:type="arc" order="49.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_BasisOfPresentationAndGoingConcernLineItems_1723" xlink:to="tsat_FinanceProvidedForFurtherSourceOfLiquidity_1959" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_BasisofPresentationandGoingConcernDetailsTable_1719" xlink:to="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1960" />
    <link:definitionArc xlink:type="arc" order="51.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1960" xlink:to="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1961_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="tsat_LiquidityAxis_1720" xlink:to="tsat_LiquidityDomainDomain_1721_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/SegmentInformationDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoSignificantCustomersMember" xlink:label="tsat_TwoSignificantCustomersMember_1734" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OneSignificantCustomersMember" xlink:label="tsat_OneSignificantCustomersMember_1735" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SegmentInformationDetailsTable" xlink:label="tsat_SegmentInformationDetailsTable_1728" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MajorCustomersAxis" xlink:label="ifrs-full_MajorCustomersAxis_1732" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MajorCustomersDomain" xlink:label="ifrs-full_MajorCustomersDomain_1733" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfOperatingSegmentsLineItems" xlink:label="ifrs-full_DisclosureOfOperatingSegmentsLineItems_1736" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NumberOfOperatingsSegment" xlink:label="tsat_NumberOfOperatingsSegment_1737" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PercentageOfEntitysRevenue" xlink:label="ifrs-full_PercentageOfEntitysRevenue_1738" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Revenue" xlink:label="ifrs-full_Revenue_1739" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MajorCustomersDomain" xlink:label="ifrs-full_MajorCustomersDomain_1733_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MajorCustomersDomain_1733" xlink:to="tsat_TwoSignificantCustomersMember_1734" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MajorCustomersDomain_1733" xlink:to="tsat_OneSignificantCustomersMember_1735" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfOperatingSegmentsLineItems_1736" xlink:to="tsat_SegmentInformationDetailsTable_1728" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_SegmentInformationDetailsTable_1728" xlink:to="ifrs-full_MajorCustomersAxis_1732" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_MajorCustomersAxis_1732" xlink:to="ifrs-full_MajorCustomersDomain_1733" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfOperatingSegmentsLineItems_1736" xlink:to="tsat_NumberOfOperatingsSegment_1737" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfOperatingSegmentsLineItems_1736" xlink:to="ifrs-full_PercentageOfEntitysRevenue_1738" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfOperatingSegmentsLineItems_1736" xlink:to="ifrs-full_Revenue_1739" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_MajorCustomersAxis_1732" xlink:to="ifrs-full_MajorCustomersDomain_1733_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RSUsWithTimeCriteriaMember" xlink:label="tsat_RSUsWithTimeCriteriaMember_1486" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RSUSWithTimeAndPerformanceCriteriaMember" xlink:label="tsat_RSUSWithTimeAndPerformanceCriteriaMember_1487" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OmnibusPlanMember" xlink:label="tsat_OmnibusPlanMember_1483" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis" xlink:label="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1484" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems" xlink:label="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RestrictedShareUnitsWithTimeCriteriaOutstanding" xlink:label="tsat_RestrictedShareUnitsWithTimeCriteriaOutstanding_1489" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PSUsWithTimeAndPerformanceCriteria" xlink:label="tsat_PSUsWithTimeAndPerformanceCriteria_1490" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferreddStockUnits" xlink:label="tsat_DeferreddStockUnits_1491" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RestrictedShareUnitsWithTimeCriteriaGranted" xlink:label="tsat_RestrictedShareUnitsWithTimeCriteriaGranted_1492" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PSUsWithTimeAndPerformanceCriteriaGranteds" xlink:label="tsat_PSUsWithTimeAndPerformanceCriteriaGranteds_1493" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredStockGranted" xlink:label="tsat_DeferredStockGranted_1494" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NumberOfInstrumentsOtherEquityInstrumentssettled" xlink:label="tsat_NumberOfInstrumentsOtherEquityInstrumentssettled_1495" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PSUsWithTimeAndPerformanceCriteriaSettled" xlink:label="tsat_PSUsWithTimeAndPerformanceCriteriaSettled_1496" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetailsTable" xlink:label="tsat_ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetailsTable_1481" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1482" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain" xlink:label="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1485" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredStockForfeited" xlink:label="tsat_DeferredStockForfeited_1934" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RestrictedShareUnitsWithTimeCriteriaForfeited" xlink:label="tsat_RestrictedShareUnitsWithTimeCriteriaForfeited_1935" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PSUsWithTimeAndPerformanceCriteriaForfeited" xlink:label="tsat_PSUsWithTimeAndPerformanceCriteriaForfeited_1936" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredStockSettled" xlink:label="tsat_DeferredStockSettled_1497" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1905" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain" xlink:label="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1485_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1905_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1485" xlink:to="tsat_RSUsWithTimeCriteriaMember_1486" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1485" xlink:to="tsat_RSUSWithTimeAndPerformanceCriteriaMember_1487" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1905" xlink:to="tsat_OmnibusPlanMember_1483" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetailsTable_1481" xlink:to="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1484" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_RestrictedShareUnitsWithTimeCriteriaOutstanding_1489" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_PSUsWithTimeAndPerformanceCriteria_1490" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_DeferreddStockUnits_1491" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_RestrictedShareUnitsWithTimeCriteriaGranted_1492" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_PSUsWithTimeAndPerformanceCriteriaGranteds_1493" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_DeferredStockGranted_1494" />
    <link:definitionArc xlink:type="arc" order="20.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_NumberOfInstrumentsOtherEquityInstrumentssettled_1495" />
    <link:definitionArc xlink:type="arc" order="21.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_PSUsWithTimeAndPerformanceCriteriaSettled_1496" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetailsTable_1481" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareBasedCompensationPlansScheduleofMovementinShareUnitsDetailsTable_1481" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1482" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1484" xlink:to="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1485" />
    <link:definitionArc xlink:type="arc" order="19.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_DeferredStockForfeited_1934" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_RestrictedShareUnitsWithTimeCriteriaForfeited_1935" />
    <link:definitionArc xlink:type="arc" order="18.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_PSUsWithTimeAndPerformanceCriteriaForfeited_1936" />
    <link:definitionArc xlink:type="arc" order="22.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems_1488" xlink:to="tsat_DeferredStockSettled_1497" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1482" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1905" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1484" xlink:to="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1485_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1482" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1905_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember" xlink:label="ifrs-full_CarryingAmountMember_1547" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CarryingAmount1Member" xlink:label="tsat_CarryingAmount1Member_1548" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ContractualCashFlowsundiscountedMember" xlink:label="tsat_ContractualCashFlowsundiscountedMember_1559" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanFiveYearsMember_1565" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotLaterThanOneYearMember" xlink:label="ifrs-full_NotLaterThanOneYearMember_1560" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember" xlink:label="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1561" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember" xlink:label="ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember_1562" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember" xlink:label="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1563" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanThreeYearsAndNotLaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanThreeYearsAndNotLaterThanFiveYearsMember_1564" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TradeAndOtherPayablesMember" xlink:label="tsat_TradeAndOtherPayablesMember_1551" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CustomerAndOtherDepositsMember" xlink:label="tsat_CustomerAndOtherDepositsMember_1552" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SatellitePerformanceIncentivePaymentsMember" xlink:label="tsat_SatellitePerformanceIncentivePaymentsMember_1553" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DerivativeLiabilitiesMember" xlink:label="tsat_DerivativeLiabilitiesMember_1554" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherFinancialLiabilitiesMember" xlink:label="tsat_OtherFinancialLiabilitiesMember_1555" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessMember" xlink:label="tsat_IndebtednessMember_1556" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1549" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityAxis" xlink:label="ifrs-full_MaturityAxis_1557" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1558" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems" xlink:label="ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_1566" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GrossLoanCommitments" xlink:label="ifrs-full_GrossLoanCommitments_1567" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetailsTable" xlink:label="tsat_FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetailsTable_1545" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis" xlink:label="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1546" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember" xlink:label="ifrs-full_CarryingAmountMember_1547_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1558_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1546" xlink:to="ifrs-full_CarryingAmountMember_1547" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_CarryingAmountMember_1547" xlink:to="tsat_CarryingAmount1Member_1548" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1558" xlink:to="tsat_ContractualCashFlowsundiscountedMember_1559" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1558" xlink:to="ifrs-full_LaterThanFiveYearsMember_1565" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1558" xlink:to="ifrs-full_NotLaterThanOneYearMember_1560" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1558" xlink:to="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1561" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1558" xlink:to="ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember_1562" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1558" xlink:to="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1563" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1558" xlink:to="ifrs-full_LaterThanThreeYearsAndNotLaterThanFiveYearsMember_1564" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" xlink:to="tsat_TradeAndOtherPayablesMember_1551" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" xlink:to="tsat_CustomerAndOtherDepositsMember_1552" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" xlink:to="tsat_SatellitePerformanceIncentivePaymentsMember_1553" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" xlink:to="tsat_DerivativeLiabilitiesMember_1554" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" xlink:to="tsat_OtherFinancialLiabilitiesMember_1555" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" xlink:to="tsat_IndebtednessMember_1556" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetailsTable_1545" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1549" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1549" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetailsTable_1545" xlink:to="ifrs-full_MaturityAxis_1557" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_MaturityAxis_1557" xlink:to="ifrs-full_MaturityDomain_1558" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_1566" xlink:to="ifrs-full_GrossLoanCommitments_1567" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_1566" xlink:to="tsat_FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetailsTable_1545" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofContractualMaturitiesofFinancialLiabilitiesDetailsTable_1545" xlink:to="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1546" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1546" xlink:to="ifrs-full_CarryingAmountMember_1547_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1549" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1550_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_MaturityAxis_1557" xlink:to="ifrs-full_MaturityDomain_1558_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareCapitalDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassCCommonSharesMember" xlink:label="tsat_ClassCCommonSharesMember_1799" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GoldenShareMember" xlink:label="tsat_GoldenShareMember_1800" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RestrictedShareUnitsMember" xlink:label="ifrs-full_RestrictedShareUnitsMember_1803" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassACommonSharesMember" xlink:label="tsat_ClassACommonSharesMember_1797" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassBCommonSharesMember" xlink:label="tsat_ClassBCommonSharesMember_1798" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PerformanceShareUnitsMember" xlink:label="tsat_PerformanceShareUnitsMember_1804" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredShareUnitsMember" xlink:label="tsat_DeferredShareUnitsMember_1805" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassALimitedPartnershipUnitsMember" xlink:label="tsat_ClassALimitedPartnershipUnitsMember_1806" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfAntidilutiveInstrumentsAxis" xlink:label="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1801" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfAntidilutiveInstrumentsDomain" xlink:label="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfClassesOfShareCapitalLineItems" xlink:label="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CommonStocksVotingRights" xlink:label="tsat_CommonStocksVotingRights_1808" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SettlementOfRestrictedStockUnit" xlink:label="tsat_SettlementOfRestrictedStockUnit_1809" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SettlementOfPublicShares" xlink:label="tsat_SettlementOfPublicShares_1810" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PerformanceShareUnits" xlink:label="tsat_PerformanceShareUnits_1811" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfSharesIssued" xlink:label="ifrs-full_NumberOfSharesIssued_1812" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfShareOptionsExercisedInSharebasedPaymentArrangement" xlink:label="ifrs-full_NumberOfShareOptionsExercisedInSharebasedPaymentArrangement_1813" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareCapitalDetailsTable" xlink:label="tsat_ShareCapitalDetailsTable_1794" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis" xlink:label="ifrs-full_ClassesOfShareCapitalAxis_1795" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1796" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfAntidilutiveInstrumentsDomain" xlink:label="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1796_default" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1796" xlink:to="tsat_ClassCCommonSharesMember_1799" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1796" xlink:to="tsat_GoldenShareMember_1800" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802" xlink:to="ifrs-full_RestrictedShareUnitsMember_1803" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1796" xlink:to="tsat_ClassACommonSharesMember_1797" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1796" xlink:to="tsat_ClassBCommonSharesMember_1798" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802" xlink:to="tsat_PerformanceShareUnitsMember_1804" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802" xlink:to="tsat_DeferredShareUnitsMember_1805" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802" xlink:to="tsat_ClassALimitedPartnershipUnitsMember_1806" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareCapitalDetailsTable_1794" xlink:to="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1801" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1801" xlink:to="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" xlink:to="tsat_CommonStocksVotingRights_1808" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" xlink:to="tsat_SettlementOfRestrictedStockUnit_1809" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" xlink:to="tsat_SettlementOfPublicShares_1810" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" xlink:to="tsat_PerformanceShareUnits_1811" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" xlink:to="ifrs-full_NumberOfSharesIssued_1812" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" xlink:to="ifrs-full_NumberOfShareOptionsExercisedInSharebasedPaymentArrangement_1813" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1807" xlink:to="tsat_ShareCapitalDetailsTable_1794" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareCapitalDetailsTable_1794" xlink:to="ifrs-full_ClassesOfShareCapitalAxis_1795" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1795" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1796" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1801" xlink:to="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1802_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1795" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1796_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/EarningsPerShareScheduleofReconciliationsoftheDenominatorsoftheBasicandDilutedPerShareDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DSUsMember" xlink:label="tsat_DSUsMember_1942" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PSUsMember" xlink:label="tsat_PSUsMember_1943" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RestrictedShareUnitsMember" xlink:label="ifrs-full_RestrictedShareUnitsMember_1945" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ShareOptionsMember" xlink:label="ifrs-full_ShareOptionsMember_1511" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DilutiveEffectOfShareOptionsOnNumberOfOrdinaryShares" xlink:label="ifrs-full_DilutiveEffectOfShareOptionsOnNumberOfOrdinaryShares_1516" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AdjustedWeightedAverageShares" xlink:label="ifrs-full_AdjustedWeightedAverageShares_1517" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_EarningsPerShareScheduleofReconciliationsoftheDenominatorsoftheBasicandDilutedPerShareDetailsTable" xlink:label="tsat_EarningsPerShareScheduleofReconciliationsoftheDenominatorsoftheBasicandDilutedPerShareDetailsTable_1508" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfAntidilutiveInstrumentsAxis" xlink:label="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1509" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfAntidilutiveInstrumentsDomain" xlink:label="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_EarningsPerShareLineItems" xlink:label="ifrs-full_EarningsPerShareLineItems_1513" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_WeightedAverageShares" xlink:label="ifrs-full_WeightedAverageShares_1514" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfAntidilutiveInstrumentsDomain" xlink:label="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510_default" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510" xlink:to="tsat_DSUsMember_1942" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510" xlink:to="tsat_PSUsMember_1943" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510" xlink:to="ifrs-full_RestrictedShareUnitsMember_1945" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510" xlink:to="ifrs-full_ShareOptionsMember_1511" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_EarningsPerShareLineItems_1513" xlink:to="ifrs-full_DilutiveEffectOfShareOptionsOnNumberOfOrdinaryShares_1516" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_EarningsPerShareLineItems_1513" xlink:to="ifrs-full_AdjustedWeightedAverageShares_1517" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_EarningsPerShareLineItems_1513" xlink:to="tsat_EarningsPerShareScheduleofReconciliationsoftheDenominatorsoftheBasicandDilutedPerShareDetailsTable_1508" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_EarningsPerShareScheduleofReconciliationsoftheDenominatorsoftheBasicandDilutedPerShareDetailsTable_1508" xlink:to="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1509" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1509" xlink:to="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_EarningsPerShareLineItems_1513" xlink:to="ifrs-full_WeightedAverageShares_1514" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_TypesOfAntidilutiveInstrumentsAxis_1509" xlink:to="ifrs-full_TypesOfAntidilutiveInstrumentsDomain_1510_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanThreeYearsAndNotLaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanThreeYearsAndNotLaterThanFiveYearsMember_1535" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanFiveYearsMember_1536" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember" xlink:label="ifrs-full_CarryingAmountMember_1527" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CarryingAmount1Member" xlink:label="tsat_CarryingAmount1Member_1528" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotLaterThanOneYearMember" xlink:label="ifrs-full_NotLaterThanOneYearMember_1531" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember" xlink:label="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1532" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanOneYearAndNotLaterThanThreeYearsMember" xlink:label="ifrs-full_LaterThanOneYearAndNotLaterThanThreeYearsMember_1533" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember" xlink:label="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1534" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems" xlink:label="ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems_1537" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CashAndCashEquivalentsIfDifferentFromStatementOfFinancialPosition" xlink:label="ifrs-full_CashAndCashEquivalentsIfDifferentFromStatementOfFinancialPosition_1538" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NoncurrentReceivables" xlink:label="ifrs-full_NoncurrentReceivables_1539" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredReceivable" xlink:label="tsat_DeferredReceivable_1540" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetailsTable" xlink:label="tsat_FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetailsTable_1525" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis" xlink:label="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1526" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityAxis" xlink:label="ifrs-full_MaturityAxis_1529" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1530" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherFinancialAssets" xlink:label="ifrs-full_OtherFinancialAssets_1541" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialAssets" xlink:label="ifrs-full_FinancialAssets_1542" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CarryingAmountMember" xlink:label="ifrs-full_CarryingAmountMember_1527_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1530_default" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1530" xlink:to="ifrs-full_LaterThanThreeYearsAndNotLaterThanFiveYearsMember_1535" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1530" xlink:to="ifrs-full_LaterThanFiveYearsMember_1536" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1526" xlink:to="ifrs-full_CarryingAmountMember_1527" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_CarryingAmountMember_1527" xlink:to="tsat_CarryingAmount1Member_1528" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1530" xlink:to="ifrs-full_NotLaterThanOneYearMember_1531" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1530" xlink:to="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1532" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1530" xlink:to="ifrs-full_LaterThanOneYearAndNotLaterThanThreeYearsMember_1533" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1530" xlink:to="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1534" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems_1537" xlink:to="ifrs-full_CashAndCashEquivalentsIfDifferentFromStatementOfFinancialPosition_1538" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems_1537" xlink:to="ifrs-full_NoncurrentReceivables_1539" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems_1537" xlink:to="tsat_DeferredReceivable_1540" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems_1537" xlink:to="tsat_FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetailsTable_1525" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetailsTable_1525" xlink:to="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1526" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofMaturityofFinancialAssetsDetailsTable_1525" xlink:to="ifrs-full_MaturityAxis_1529" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_MaturityAxis_1529" xlink:to="ifrs-full_MaturityDomain_1530" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems_1537" xlink:to="ifrs-full_OtherFinancialAssets_1541" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForFinancialAssetsHeldForManagingLiquidityRiskLineItems_1537" xlink:to="ifrs-full_FinancialAssets_1542" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis_1526" xlink:to="ifrs-full_CarryingAmountMember_1527_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_MaturityAxis_1529" xlink:to="ifrs-full_MaturityDomain_1530_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/SegmentInformationScheduleofEquipmentSalesDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GEOMember" xlink:label="tsat_GEOMember_1313" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LEOMember" xlink:label="tsat_LEOMember_1314" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems" xlink:label="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1315" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RevenueFromSaleOfTelecommunicationEquipment" xlink:label="ifrs-full_RevenueFromSaleOfTelecommunicationEquipment_1316" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SegmentInformationScheduleofEquipmentSalesDetailsTable" xlink:label="tsat_SegmentInformationScheduleofEquipmentSalesDetailsTable_1310" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SegmentsAxis" xlink:label="ifrs-full_SegmentsAxis_1311" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SegmentsDomain" xlink:label="ifrs-full_SegmentsDomain_1312" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_SegmentsDomain" xlink:label="ifrs-full_SegmentsDomain_1312_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_SegmentsDomain_1312" xlink:to="tsat_GEOMember_1313" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_SegmentsDomain_1312" xlink:to="tsat_LEOMember_1314" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1315" xlink:to="ifrs-full_RevenueFromSaleOfTelecommunicationEquipment_1316" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems_1315" xlink:to="tsat_SegmentInformationScheduleofEquipmentSalesDetailsTable_1310" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_SegmentInformationScheduleofEquipmentSalesDetailsTable_1310" xlink:to="ifrs-full_SegmentsAxis_1311" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_SegmentsAxis_1311" xlink:to="ifrs-full_SegmentsDomain_1312" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_SegmentsAxis_1311" xlink:to="ifrs-full_SegmentsDomain_1312_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/SegmentInformationScheduleofGeographicRegionsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_AllOthersMember" xlink:label="tsat_AllOthersMember_1328" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_EuropeMiddleEastAfricaMember" xlink:label="tsat_EuropeMiddleEastAfricaMember_1324" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LatinAmericaCaribbeanMember" xlink:label="tsat_LatinAmericaCaribbeanMember_1325" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_AsiaAustraliaMember" xlink:label="tsat_AsiaAustraliaMember_1326" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SegmentInformationScheduleofGeographicRegionsDetailsTable" xlink:label="tsat_SegmentInformationScheduleofGeographicRegionsDetailsTable_1319" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfGeographicalAreasLineItems" xlink:label="ifrs-full_DisclosureOfGeographicalAreasLineItems_1329" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Revenue" xlink:label="ifrs-full_Revenue_1330" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PropertyPlantAndEquipment" xlink:label="ifrs-full_PropertyPlantAndEquipment_1331" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IntangibleAssetsOtherThanGoodwill" xlink:label="ifrs-full_IntangibleAssetsOtherThanGoodwill_1332" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherNoncurrentNonfinancialAssets" xlink:label="ifrs-full_OtherNoncurrentNonfinancialAssets_1333" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasAxis" xlink:label="ifrs-full_GeographicalAreasAxis_1320" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasDomain" xlink:label="ifrs-full_GeographicalAreasDomain_1321" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CA" xlink:label="country_CA_1322" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US" xlink:label="country_US_1323" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_GB" xlink:label="country_GB_1327" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_GeographicalAreasDomain" xlink:label="ifrs-full_GeographicalAreasDomain_1321_default" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_GeographicalAreasDomain_1321" xlink:to="tsat_AllOthersMember_1328" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_GeographicalAreasDomain_1321" xlink:to="tsat_EuropeMiddleEastAfricaMember_1324" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_GeographicalAreasDomain_1321" xlink:to="tsat_LatinAmericaCaribbeanMember_1325" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_GeographicalAreasDomain_1321" xlink:to="tsat_AsiaAustraliaMember_1326" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfGeographicalAreasLineItems_1329" xlink:to="tsat_SegmentInformationScheduleofGeographicRegionsDetailsTable_1319" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfGeographicalAreasLineItems_1329" xlink:to="ifrs-full_Revenue_1330" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfGeographicalAreasLineItems_1329" xlink:to="ifrs-full_PropertyPlantAndEquipment_1331" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfGeographicalAreasLineItems_1329" xlink:to="ifrs-full_IntangibleAssetsOtherThanGoodwill_1332" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfGeographicalAreasLineItems_1329" xlink:to="ifrs-full_OtherNoncurrentNonfinancialAssets_1333" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_SegmentInformationScheduleofGeographicRegionsDetailsTable_1319" xlink:to="ifrs-full_GeographicalAreasAxis_1320" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_GeographicalAreasAxis_1320" xlink:to="ifrs-full_GeographicalAreasDomain_1321" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_GeographicalAreasDomain_1321" xlink:to="country_CA_1322" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_GeographicalAreasDomain_1321" xlink:to="country_US_1323" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_GeographicalAreasDomain_1321" xlink:to="country_GB_1327" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_GeographicalAreasAxis_1320" xlink:to="ifrs-full_GeographicalAreasDomain_1321_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/IndebtednessScheduleofIndebtednessDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TermLoanBUSFacilityMember" xlink:label="tsat_TermLoanBUSFacilityMember_1391" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember" xlink:label="tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember_1392" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySixSeniorSecuredNotesMember" xlink:label="tsat_TwoThousandTwentySixSeniorSecuredNotesMember_1393" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySevenSeniorSecuredNotesMember" xlink:label="tsat_TwoThousandTwentySevenSeniorSecuredNotesMember_1394" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentOfCanadaTelesatLightspeedFinancingMember" xlink:label="tsat_GovernmentOfCanadaTelesatLightspeedFinancingMember_1395" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentOfQuebecTelesatLightspeedFinancingMember" xlink:label="tsat_GovernmentOfQuebecTelesatLightspeedFinancingMember_1396" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatGEOFinancingMember" xlink:label="tsat_TelesatGEOFinancingMember_1399" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfCreditRiskExposureLineItems" xlink:label="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1400" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatGeoFinancingAbstract" xlink:label="tsat_TelesatGeoFinancingAbstract_1401" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BorrowingsBeforeDeferredFinancingCosts" xlink:label="tsat_BorrowingsBeforeDeferredFinancingCosts_1402" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredFinancingCostsPrepaymentOptionAndLossOnRepayment" xlink:label="tsat_DeferredFinancingCostsPrepaymentOptionAndLossOnRepayment_1403" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Borrowings" xlink:label="ifrs-full_Borrowings_1404" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessScheduleofIndebtednessDetailsTable" xlink:label="tsat_IndebtednessScheduleofIndebtednessDetailsTable_1388" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsAxis" xlink:label="tsat_DebtInstrumentsAxis_1389" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsDomainDomain" xlink:label="tsat_DebtInstrumentsDomainDomain_1390" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis" xlink:label="ifrs-full_BorrowingsByNameAxis_1397" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain" xlink:label="ifrs-full_BorrowingsByNameDomain_1398" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ShorttermBorrowings" xlink:label="ifrs-full_ShorttermBorrowings_1405" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LongtermBorrowings" xlink:label="ifrs-full_LongtermBorrowings_1406" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsDomainDomain" xlink:label="tsat_DebtInstrumentsDomainDomain_1390_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain" xlink:label="ifrs-full_BorrowingsByNameDomain_1398_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1390" xlink:to="tsat_TermLoanBUSFacilityMember_1391" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1390" xlink:to="tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember_1392" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1390" xlink:to="tsat_TwoThousandTwentySixSeniorSecuredNotesMember_1393" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1390" xlink:to="tsat_TwoThousandTwentySevenSeniorSecuredNotesMember_1394" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1390" xlink:to="tsat_GovernmentOfCanadaTelesatLightspeedFinancingMember_1395" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1390" xlink:to="tsat_GovernmentOfQuebecTelesatLightspeedFinancingMember_1396" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1398" xlink:to="tsat_TelesatGEOFinancingMember_1399" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1400" xlink:to="tsat_TelesatGeoFinancingAbstract_1401" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_TelesatGeoFinancingAbstract_1401" xlink:to="tsat_BorrowingsBeforeDeferredFinancingCosts_1402" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1400" xlink:to="tsat_DeferredFinancingCostsPrepaymentOptionAndLossOnRepayment_1403" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1400" xlink:to="ifrs-full_Borrowings_1404" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1400" xlink:to="tsat_IndebtednessScheduleofIndebtednessDetailsTable_1388" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_IndebtednessScheduleofIndebtednessDetailsTable_1388" xlink:to="tsat_DebtInstrumentsAxis_1389" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="tsat_DebtInstrumentsAxis_1389" xlink:to="tsat_DebtInstrumentsDomainDomain_1390" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_IndebtednessScheduleofIndebtednessDetailsTable_1388" xlink:to="ifrs-full_BorrowingsByNameAxis_1397" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_BorrowingsByNameAxis_1397" xlink:to="ifrs-full_BorrowingsByNameDomain_1398" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1400" xlink:to="ifrs-full_ShorttermBorrowings_1405" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1400" xlink:to="ifrs-full_LongtermBorrowings_1406" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="tsat_DebtInstrumentsAxis_1389" xlink:to="tsat_DebtInstrumentsDomainDomain_1390_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_BorrowingsByNameAxis_1397" xlink:to="ifrs-full_BorrowingsByNameDomain_1398_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails3" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassBLPUnitsMember" xlink:label="tsat_ClassBLPUnitsMember_1458" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassCLPUnitsMember" xlink:label="tsat_ClassCLPUnitsMember_1459" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LimitedPartnershipUnitsMember" xlink:label="tsat_LimitedPartnershipUnitsMember_1455" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfClassesOfShareCapitalLineItems" xlink:label="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1460" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfSharesOutstanding" xlink:label="ifrs-full_NumberOfSharesOutstanding_1461" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssuedCapital" xlink:label="ifrs-full_IssuedCapital_1462" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable" xlink:label="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1453" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis_1454" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis" xlink:label="ifrs-full_ClassesOfShareCapitalAxis_1456" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1457" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_1902" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1457_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_1902_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1457" xlink:to="tsat_ClassBLPUnitsMember_1458" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1457" xlink:to="tsat_ClassCLPUnitsMember_1459" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain_1902" xlink:to="tsat_LimitedPartnershipUnitsMember_1455" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1460" xlink:to="ifrs-full_NumberOfSharesOutstanding_1461" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1460" xlink:to="ifrs-full_IssuedCapital_1462" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1460" xlink:to="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1453" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1453" xlink:to="srt_CounterpartyNameAxis_1454" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1453" xlink:to="ifrs-full_ClassesOfShareCapitalAxis_1456" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1456" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1457" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_CounterpartyNameAxis_1454" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_1902" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1456" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1457_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_CounterpartyNameAxis_1454" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_1902_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TimeVestingOptionPlansMember" xlink:label="tsat_TimeVestingOptionPlansMember_1470" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PerformanceVestingOptionPlansMember" xlink:label="tsat_PerformanceVestingOptionPlansMember_1471" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_HistoricPlanMember" xlink:label="tsat_HistoricPlanMember_1467" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OmnibusPlanMember" xlink:label="tsat_OmnibusPlanMember_1468" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis" xlink:label="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1469" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems" xlink:label="ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1472" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfSharesOutstanding" xlink:label="ifrs-full_NumberOfSharesOutstanding_1473" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetailsTable" xlink:label="tsat_ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetailsTable_1465" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1466" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_WeightedAverageExercisePriceOfShareOptionsOutstandingInSharebasedPaymentArrangement2019" xlink:label="ifrs-full_WeightedAverageExercisePriceOfShareOptionsOutstandingInSharebasedPaymentArrangement2019_1474" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfShareOptionsExercisedInSharebasedPaymentArrangement" xlink:label="ifrs-full_NumberOfShareOptionsExercisedInSharebasedPaymentArrangement_1475" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_WeightedAverageExercisePriceOfShareOptionsExercisedInSharebasedPaymentArrangement2019" xlink:label="ifrs-full_WeightedAverageExercisePriceOfShareOptionsExercisedInSharebasedPaymentArrangement2019_1476" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1903" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain" xlink:label="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1904" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1903_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain" xlink:label="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1904_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1904" xlink:to="tsat_TimeVestingOptionPlansMember_1470" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1904" xlink:to="tsat_PerformanceVestingOptionPlansMember_1471" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1903" xlink:to="tsat_HistoricPlanMember_1467" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1903" xlink:to="tsat_OmnibusPlanMember_1468" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetailsTable_1465" xlink:to="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1469" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1472" xlink:to="ifrs-full_NumberOfSharesOutstanding_1473" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1472" xlink:to="tsat_ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetailsTable_1465" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareBasedCompensationPlansScheduleofNumberofTimeVestingStockOptionsOutstandingandtheirWeightedAverageExercisePriceDetailsTable_1465" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1466" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1472" xlink:to="ifrs-full_WeightedAverageExercisePriceOfShareOptionsOutstandingInSharebasedPaymentArrangement2019_1474" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1472" xlink:to="ifrs-full_NumberOfShareOptionsExercisedInSharebasedPaymentArrangement_1475" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems_1472" xlink:to="ifrs-full_WeightedAverageExercisePriceOfShareOptionsExercisedInSharebasedPaymentArrangement2019_1476" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1466" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1903" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1469" xlink:to="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1904" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1466" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1903_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis_1469" xlink:to="ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsDomain_1904_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/GoodwillandIntangibleAssetsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember" xlink:label="ifrs-full_TopOfRangeMember_1756" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember" xlink:label="ifrs-full_BottomOfRangeMember_1757" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GoodwillandIntangibleAssetsDetailsTable" xlink:label="tsat_GoodwillandIntangibleAssetsDetailsTable_1753" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis" xlink:label="ifrs-full_RangeAxis_1754" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain" xlink:label="ifrs-full_RangeDomain_1755" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfIntangibleAssetsLineItems" xlink:label="ifrs-full_DisclosureOfIntangibleAssetsLineItems_1758" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PercentageOfDiscountRateOfGoodwillImpairment" xlink:label="tsat_PercentageOfDiscountRateOfGoodwillImpairment_1759" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_AdjustmentsForImpairmentLossRecognisedInProfitOrLossGoodwill" xlink:label="ifrs-full_AdjustmentsForImpairmentLossRecognisedInProfitOrLossGoodwill_1760" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PercentageOfGoodwillImpairmentLoss" xlink:label="tsat_PercentageOfGoodwillImpairmentLoss_1949" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain" xlink:label="ifrs-full_RangeDomain_1755_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangeDomain_1755" xlink:to="ifrs-full_TopOfRangeMember_1756" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangeDomain_1755" xlink:to="ifrs-full_BottomOfRangeMember_1757" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfIntangibleAssetsLineItems_1758" xlink:to="tsat_GoodwillandIntangibleAssetsDetailsTable_1753" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_GoodwillandIntangibleAssetsDetailsTable_1753" xlink:to="ifrs-full_RangeAxis_1754" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_RangeAxis_1754" xlink:to="ifrs-full_RangeDomain_1755" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfIntangibleAssetsLineItems_1758" xlink:to="tsat_PercentageOfDiscountRateOfGoodwillImpairment_1759" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfIntangibleAssetsLineItems_1758" xlink:to="ifrs-full_AdjustmentsForImpairmentLossRecognisedInProfitOrLossGoodwill_1760" />
    <link:definitionArc xlink:type="arc" order="45.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfIntangibleAssetsLineItems_1758" xlink:to="tsat_PercentageOfGoodwillImpairmentLoss_1949" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_RangeAxis_1754" xlink:to="ifrs-full_RangeDomain_1755_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/IndebtednessDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SeniorSecuredCreditFacilitiesMember" xlink:label="tsat_SeniorSecuredCreditFacilitiesMember_1770" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TermLoanBUSFacilityMember" xlink:label="tsat_TermLoanBUSFacilityMember_1771" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SixPointFivePercentSeniorNotesMember" xlink:label="tsat_SixPointFivePercentSeniorNotesMember_1781" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatLightspeedFinancingWarrantsMember" xlink:label="tsat_TelesatLightspeedFinancingWarrantsMember_1774" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatLightspeedFinancingMember" xlink:label="tsat_TelesatLightspeedFinancingMember_1775" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember" xlink:label="tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember_1919" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySixSeniorSecuredNotesMember" xlink:label="tsat_TwoThousandTwentySixSeniorSecuredNotesMember_1920" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySevenSeniorSecuredNotesMember" xlink:label="tsat_TwoThousandTwentySevenSeniorSecuredNotesMember_1921" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentOfCanadaMember" xlink:label="tsat_GovernmentOfCanadaMember_1925" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentOfQuebecMember" xlink:label="tsat_GovernmentOfQuebecMember_1926" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PrivatePlacementsMember" xlink:label="tsat_PrivatePlacementsMember_1778" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessDetailsTable" xlink:label="tsat_IndebtednessDetailsTable_1767" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsAxis" xlink:label="tsat_DebtInstrumentsAxis_1768" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsDomainDomain" xlink:label="tsat_DebtInstrumentsDomainDomain_1769" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessLineItems" xlink:label="tsat_IndebtednessLineItems_1782" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RevolvingCreditFacility" xlink:label="tsat_RevolvingCreditFacility_1783" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_CreditsExposure" xlink:label="tsat_CreditsExposure_1784" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Borrowings" xlink:label="ifrs-full_Borrowings_1785" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsInterestRate" xlink:label="ifrs-full_BorrowingsInterestRate_1786" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BorrowingsMaturityDateDescription" xlink:label="tsat_BorrowingsMaturityDateDescription_1787" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RepurchasedPrincipalAmount" xlink:label="tsat_RepurchasedPrincipalAmount_1788" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SaleOfStockAxis" xlink:label="tsat_SaleOfStockAxis_1776" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SaleOfStockDomainDomain" xlink:label="tsat_SaleOfStockDomainDomain_1777" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OpenMarketPurchases" xlink:label="tsat_OpenMarketPurchases_1922" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_PaymentsForDebtIssueCosts" xlink:label="ifrs-full_PaymentsForDebtIssueCosts_1923" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestExpenseOnBorrowings" xlink:label="ifrs-full_InterestExpenseOnBorrowings_1924" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_WarrantsAndRightsOutstandingTerms" xlink:label="tsat_WarrantsAndRightsOutstandingTerms_1927" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis" xlink:label="ifrs-full_BorrowingsByNameAxis_1779" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain" xlink:label="ifrs-full_BorrowingsByNameDomain_1780" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RepurchaseOfPrincipalAmount" xlink:label="tsat_RepurchaseOfPrincipalAmount_1789" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtExchange" xlink:label="tsat_DebtExchange_1918" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsDomainDomain" xlink:label="tsat_DebtInstrumentsDomainDomain_1769_default" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SaleOfStockDomainDomain" xlink:label="tsat_SaleOfStockDomainDomain_1777_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain" xlink:label="ifrs-full_BorrowingsByNameDomain_1780_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1769" xlink:to="tsat_SeniorSecuredCreditFacilitiesMember_1770" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1769" xlink:to="tsat_TermLoanBUSFacilityMember_1771" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1780" xlink:to="tsat_SixPointFivePercentSeniorNotesMember_1781" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1769" xlink:to="tsat_TelesatLightspeedFinancingWarrantsMember_1774" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1769" xlink:to="tsat_TelesatLightspeedFinancingMember_1775" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1769" xlink:to="tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember_1919" />
    <link:definitionArc xlink:type="arc" order="18.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1769" xlink:to="tsat_TwoThousandTwentySixSeniorSecuredNotesMember_1920" />
    <link:definitionArc xlink:type="arc" order="19.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1769" xlink:to="tsat_TwoThousandTwentySevenSeniorSecuredNotesMember_1921" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1780" xlink:to="tsat_GovernmentOfCanadaMember_1925" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1780" xlink:to="tsat_GovernmentOfQuebecMember_1926" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_SaleOfStockDomainDomain_1777" xlink:to="tsat_PrivatePlacementsMember_1778" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_IndebtednessDetailsTable_1767" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_IndebtednessDetailsTable_1767" xlink:to="tsat_DebtInstrumentsAxis_1768" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="tsat_DebtInstrumentsAxis_1768" xlink:to="tsat_DebtInstrumentsDomainDomain_1769" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_RevolvingCreditFacility_1783" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_CreditsExposure_1784" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="ifrs-full_Borrowings_1785" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="ifrs-full_BorrowingsInterestRate_1786" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_BorrowingsMaturityDateDescription_1787" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_RepurchasedPrincipalAmount_1788" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_IndebtednessDetailsTable_1767" xlink:to="tsat_SaleOfStockAxis_1776" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="tsat_SaleOfStockAxis_1776" xlink:to="tsat_SaleOfStockDomainDomain_1777" />
    <link:definitionArc xlink:type="arc" order="30.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_OpenMarketPurchases_1922" />
    <link:definitionArc xlink:type="arc" order="31.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="ifrs-full_PaymentsForDebtIssueCosts_1923" />
    <link:definitionArc xlink:type="arc" order="32.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="ifrs-full_InterestExpenseOnBorrowings_1924" />
    <link:definitionArc xlink:type="arc" order="33.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_WarrantsAndRightsOutstandingTerms_1927" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_IndebtednessDetailsTable_1767" xlink:to="ifrs-full_BorrowingsByNameAxis_1779" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_BorrowingsByNameAxis_1779" xlink:to="ifrs-full_BorrowingsByNameDomain_1780" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_RepurchaseOfPrincipalAmount_1789" />
    <link:definitionArc xlink:type="arc" order="29.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_IndebtednessLineItems_1782" xlink:to="tsat_DebtExchange_1918" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="tsat_DebtInstrumentsAxis_1768" xlink:to="tsat_DebtInstrumentsDomainDomain_1769_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="tsat_SaleOfStockAxis_1776" xlink:to="tsat_SaleOfStockDomainDomain_1777_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_BorrowingsByNameAxis_1779" xlink:to="ifrs-full_BorrowingsByNameDomain_1780_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/FinancialInstrumentsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ForeignExchangeRiskMember" xlink:label="tsat_ForeignExchangeRiskMember_1955" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_InternationalCustomersMember" xlink:label="tsat_InternationalCustomersMember_1850" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatLightspeedWarrantsMember" xlink:label="tsat_TelesatLightspeedWarrantsMember_1853" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BottomOfRangeMember" xlink:label="ifrs-full_BottomOfRangeMember_1856" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TopOfRangeMember" xlink:label="ifrs-full_TopOfRangeMember_1857" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_InterestRatesFloorMember" xlink:label="tsat_InterestRatesFloorMember_1846" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NorthAmericanMember" xlink:label="tsat_NorthAmericanMember_1849" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ConcentrationsOfRisk" xlink:label="ifrs-full_ConcentrationsOfRisk_1860" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TradeAndOtherCurrentReceivablesAllowanceForDoubtfulAccounts" xlink:label="tsat_TradeAndOtherCurrentReceivablesAllowanceForDoubtfulAccounts_1861" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BorrowingsBeforeDeferredFinancingCost" xlink:label="tsat_BorrowingsBeforeDeferredFinancingCost_1862" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NoncurrentDerivativeFinancialLiabilities" xlink:label="ifrs-full_NoncurrentDerivativeFinancialLiabilities_1863" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredCharges" xlink:label="tsat_DeferredCharges_1864" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis_1851" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_1852" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeAxis" xlink:label="ifrs-full_RangeAxis_1854" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain" xlink:label="ifrs-full_RangeDomain_1855" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinancialInstrumentsDetailsTable" xlink:label="tsat_FinancialInstrumentsDetailsTable_1843" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialAssetsAxis" xlink:label="ifrs-full_ClassesOfFinancialAssetsAxis_1844" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialAssetsDomain" xlink:label="ifrs-full_ClassesOfFinancialAssetsDomain_1845" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis" xlink:label="srt_MajorCustomersAxis_1847" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain" xlink:label="srt_NameOfMajorCustomerDomain_1848" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DescriptionOfDiscountRatesUsedInCurrentEstimateOfValueInUse" xlink:label="ifrs-full_DescriptionOfDiscountRatesUsedInCurrentEstimateOfValueInUse_1871" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFinancialInstrumentsLineItems" xlink:label="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaximumExposureToCreditRisk" xlink:label="ifrs-full_MaximumExposureToCreditRisk_1859" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsInterestRate" xlink:label="ifrs-full_BorrowingsInterestRate_1865" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NetIncreaseIncomeImpactOfPercentIncreaseDecrease" xlink:label="tsat_NetIncreaseIncomeImpactOfPercentIncreaseDecrease_1866" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherComprehensiveIncomeLossImpactOf5PercentIncreaseDecrease" xlink:label="tsat_OtherComprehensiveIncomeLossImpactOf5PercentIncreaseDecrease_1867" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherDifferencesToCashAndCashEquivalentsInStatementOfCashFlows" xlink:label="ifrs-full_OtherDifferencesToCashAndCashEquivalentsInStatementOfCashFlows_1868" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DescriptionOfDiscountRatesAppliedToCashFlowProjections" xlink:label="ifrs-full_DescriptionOfDiscountRatesAppliedToCashFlowProjections_1870" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_1852_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_RangeDomain" xlink:label="ifrs-full_RangeDomain_1855_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialAssetsDomain" xlink:label="ifrs-full_ClassesOfFinancialAssetsDomain_1845_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain" xlink:label="srt_NameOfMajorCustomerDomain_1848_default" />
    <link:definitionArc xlink:type="arc" order="48.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialAssetsDomain_1845" xlink:to="tsat_ForeignExchangeRiskMember_1955" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_NameOfMajorCustomerDomain_1848" xlink:to="tsat_InternationalCustomersMember_1850" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain_1852" xlink:to="tsat_TelesatLightspeedWarrantsMember_1853" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangeDomain_1855" xlink:to="ifrs-full_BottomOfRangeMember_1856" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_RangeDomain_1855" xlink:to="ifrs-full_TopOfRangeMember_1857" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialAssetsDomain_1845" xlink:to="tsat_InterestRatesFloorMember_1846" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_NameOfMajorCustomerDomain_1848" xlink:to="tsat_NorthAmericanMember_1849" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="ifrs-full_ConcentrationsOfRisk_1860" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="tsat_TradeAndOtherCurrentReceivablesAllowanceForDoubtfulAccounts_1861" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="tsat_BorrowingsBeforeDeferredFinancingCost_1862" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="ifrs-full_NoncurrentDerivativeFinancialLiabilities_1863" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="tsat_DeferredCharges_1864" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsDetailsTable_1843" xlink:to="srt_CounterpartyNameAxis_1851" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_CounterpartyNameAxis_1851" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_1852" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsDetailsTable_1843" xlink:to="ifrs-full_RangeAxis_1854" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_RangeAxis_1854" xlink:to="ifrs-full_RangeDomain_1855" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="tsat_FinancialInstrumentsDetailsTable_1843" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsDetailsTable_1843" xlink:to="ifrs-full_ClassesOfFinancialAssetsAxis_1844" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfFinancialAssetsAxis_1844" xlink:to="ifrs-full_ClassesOfFinancialAssetsDomain_1845" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsDetailsTable_1843" xlink:to="srt_MajorCustomersAxis_1847" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_MajorCustomersAxis_1847" xlink:to="srt_NameOfMajorCustomerDomain_1848" />
    <link:definitionArc xlink:type="arc" order="22.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="ifrs-full_DescriptionOfDiscountRatesUsedInCurrentEstimateOfValueInUse_1871" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="ifrs-full_MaximumExposureToCreditRisk_1859" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="ifrs-full_BorrowingsInterestRate_1865" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="tsat_NetIncreaseIncomeImpactOfPercentIncreaseDecrease_1866" />
    <link:definitionArc xlink:type="arc" order="18.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="tsat_OtherComprehensiveIncomeLossImpactOf5PercentIncreaseDecrease_1867" />
    <link:definitionArc xlink:type="arc" order="19.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="ifrs-full_OtherDifferencesToCashAndCashEquivalentsInStatementOfCashFlows_1868" />
    <link:definitionArc xlink:type="arc" order="21.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFinancialInstrumentsLineItems_1858" xlink:to="ifrs-full_DescriptionOfDiscountRatesAppliedToCashFlowProjections_1870" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_CounterpartyNameAxis_1851" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_1852_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_RangeAxis_1854" xlink:to="ifrs-full_RangeDomain_1855_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfFinancialAssetsAxis_1844" xlink:to="ifrs-full_ClassesOfFinancialAssetsDomain_1845_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_MajorCustomersAxis_1847" xlink:to="srt_NameOfMajorCustomerDomain_1848_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/LeaseLiabilitiesScheduleofExpectedUndiscountedContractualCashFlowsoftheLeaseLiabilitiesDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NotLaterThanOneYearMember" xlink:label="ifrs-full_NotLaterThanOneYearMember_1378" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember" xlink:label="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1379" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember" xlink:label="ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember_1380" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember" xlink:label="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1381" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanFourYearsAndNotLaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanFourYearsAndNotLaterThanFiveYearsMember_1382" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LaterThanFiveYearsMember" xlink:label="ifrs-full_LaterThanFiveYearsMember_1383" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_LeaseLiabilitiesScheduleofExpectedUndiscountedContractualCashFlowsoftheLeaseLiabilitiesDetailsTable" xlink:label="tsat_LeaseLiabilitiesScheduleofExpectedUndiscountedContractualCashFlowsoftheLeaseLiabilitiesDetailsTable_1375" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityAxis" xlink:label="ifrs-full_MaturityAxis_1376" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1377" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfMaturityAnalysisOfOperatingLeasePaymentsLineItems" xlink:label="ifrs-full_DisclosureOfMaturityAnalysisOfOperatingLeasePaymentsLineItems_1384" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LeaseLiabilities" xlink:label="ifrs-full_LeaseLiabilities_1385" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_MaturityDomain" xlink:label="ifrs-full_MaturityDomain_1377_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1377" xlink:to="ifrs-full_NotLaterThanOneYearMember_1378" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1377" xlink:to="ifrs-full_LaterThanOneYearAndNotLaterThanTwoYearsMember_1379" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1377" xlink:to="ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember_1380" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1377" xlink:to="ifrs-full_LaterThanThreeYearsAndNotLaterThanFourYearsMember_1381" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1377" xlink:to="ifrs-full_LaterThanFourYearsAndNotLaterThanFiveYearsMember_1382" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_MaturityDomain_1377" xlink:to="ifrs-full_LaterThanFiveYearsMember_1383" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisOfOperatingLeasePaymentsLineItems_1384" xlink:to="tsat_LeaseLiabilitiesScheduleofExpectedUndiscountedContractualCashFlowsoftheLeaseLiabilitiesDetailsTable_1375" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_LeaseLiabilitiesScheduleofExpectedUndiscountedContractualCashFlowsoftheLeaseLiabilitiesDetailsTable_1375" xlink:to="ifrs-full_MaturityAxis_1376" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_MaturityAxis_1376" xlink:to="ifrs-full_MaturityDomain_1377" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisOfOperatingLeasePaymentsLineItems_1384" xlink:to="ifrs-full_LeaseLiabilities_1385" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_MaturityAxis_1376" xlink:to="ifrs-full_MaturityDomain_1377_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareBasedCompensationPlansDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_HistoricPlanMember" xlink:label="tsat_HistoricPlanMember_1940" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_EmployeeBenefitsMember" xlink:label="ifrs-full_EmployeeBenefitsMember_1826" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfShareOptionsGrantedInSharebasedPaymentArrangement" xlink:label="ifrs-full_NumberOfShareOptionsGrantedInSharebasedPaymentArrangement_1937" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsAxis" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1938" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1939" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAttributionOfSpecifiedExpensesByNatureLineItems" xlink:label="ifrs-full_DisclosureOfAttributionOfSpecifiedExpensesByNatureLineItems_1827" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_EmployeeBenefitsExpense" xlink:label="ifrs-full_EmployeeBenefitsExpense_1828" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NatureExpensesDomain" xlink:label="ifrs-full_NatureExpensesDomain_1911" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareBasedCompensationPlansDetailsTable" xlink:label="tsat_ShareBasedCompensationPlansDetailsTable_1824" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NatureExpensesAxis" xlink:label="ifrs-full_NatureExpensesAxis_1825" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TypesOfSharebasedPaymentArrangementsDomain" xlink:label="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1939_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NatureExpensesDomain" xlink:label="ifrs-full_NatureExpensesDomain_1911_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1939" xlink:to="tsat_HistoricPlanMember_1940" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_NatureExpensesDomain_1911" xlink:to="ifrs-full_EmployeeBenefitsMember_1826" />
    <link:definitionArc xlink:type="arc" order="38.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfAttributionOfSpecifiedExpensesByNatureLineItems_1827" xlink:to="ifrs-full_NumberOfShareOptionsGrantedInSharebasedPaymentArrangement_1937" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareBasedCompensationPlansDetailsTable_1824" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1938" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1938" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1939" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfAttributionOfSpecifiedExpensesByNatureLineItems_1827" xlink:to="ifrs-full_EmployeeBenefitsExpense_1828" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_NatureExpensesAxis_1825" xlink:to="ifrs-full_NatureExpensesDomain_1911" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfAttributionOfSpecifiedExpensesByNatureLineItems_1827" xlink:to="tsat_ShareBasedCompensationPlansDetailsTable_1824" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareBasedCompensationPlansDetailsTable_1824" xlink:to="ifrs-full_NatureExpensesAxis_1825" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_TypesOfSharebasedPaymentArrangementsAxis_1938" xlink:to="ifrs-full_TypesOfSharebasedPaymentArrangementsDomain_1939_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_NatureExpensesAxis_1825" xlink:to="ifrs-full_NatureExpensesDomain_1911_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialAssetsAtFairValueMember" xlink:label="ifrs-full_FinancialAssetsAtFairValueMember_1582" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Level1OfFairValueHierarchyMember" xlink:label="ifrs-full_Level1OfFairValueHierarchyMember_1585" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Level2OfFairValueHierarchyMember" xlink:label="ifrs-full_Level2OfFairValueHierarchyMember_1586" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_Level2And3OfFairValueHierarchyMember" xlink:label="ifrs-full_Level2And3OfFairValueHierarchyMember_1587" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialAssetsAtAmortisedCostCategoryMember" xlink:label="ifrs-full_FinancialAssetsAtAmortisedCostCategoryMember_1590" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember" xlink:label="ifrs-full_FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember_1591" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherNoncurrentFinancialAssets" xlink:label="ifrs-full_OtherNoncurrentFinancialAssets_1596" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TradeAndOtherPayables" xlink:label="ifrs-full_TradeAndOtherPayables_1597" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherCurrentFinancialLiabilities" xlink:label="ifrs-full_OtherCurrentFinancialLiabilities_1598" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherNoncurrentFinancialLiabilities" xlink:label="ifrs-full_OtherNoncurrentFinancialLiabilities_1599" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BorrowingsBeforeDeferredFinancingCosts" xlink:label="tsat_BorrowingsBeforeDeferredFinancingCosts_1600" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NetAssetsLiabilities" xlink:label="ifrs-full_NetAssetsLiabilities_1601" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetailsTable" xlink:label="tsat_FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetailsTable_1579" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialAssetsAxis" xlink:label="ifrs-full_ClassesOfFinancialAssetsAxis_1580" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialAssetsDomain" xlink:label="ifrs-full_ClassesOfFinancialAssetsDomain_1581" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LevelsOfFairValueHierarchyAxis" xlink:label="ifrs-full_LevelsOfFairValueHierarchyAxis_1583" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LevelsOfFairValueHierarchyDomain" xlink:label="ifrs-full_LevelsOfFairValueHierarchyDomain_1584" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialAssetsAxis" xlink:label="ifrs-full_CategoriesOfFinancialAssetsAxis_1588" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialAssetsDomain" xlink:label="ifrs-full_CategoriesOfFinancialAssetsDomain_1589" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems" xlink:label="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CashAndCashEquivalents" xlink:label="ifrs-full_CashAndCashEquivalents_1593" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_TradeAndOtherReceivables" xlink:label="ifrs-full_TradeAndOtherReceivables_1594" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherCurrentFinancialAssets" xlink:label="ifrs-full_OtherCurrentFinancialAssets_1595" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialAssetsDomain" xlink:label="ifrs-full_ClassesOfFinancialAssetsDomain_1581_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_LevelsOfFairValueHierarchyDomain" xlink:label="ifrs-full_LevelsOfFairValueHierarchyDomain_1584_default" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_CategoriesOfFinancialAssetsDomain" xlink:label="ifrs-full_CategoriesOfFinancialAssetsDomain_1589_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialAssetsDomain_1581" xlink:to="ifrs-full_FinancialAssetsAtFairValueMember_1582" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_LevelsOfFairValueHierarchyDomain_1584" xlink:to="ifrs-full_Level1OfFairValueHierarchyMember_1585" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_LevelsOfFairValueHierarchyDomain_1584" xlink:to="ifrs-full_Level2OfFairValueHierarchyMember_1586" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_LevelsOfFairValueHierarchyDomain_1584" xlink:to="ifrs-full_Level2And3OfFairValueHierarchyMember_1587" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_CategoriesOfFinancialAssetsDomain_1589" xlink:to="ifrs-full_FinancialAssetsAtAmortisedCostCategoryMember_1590" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_CategoriesOfFinancialAssetsDomain_1589" xlink:to="ifrs-full_FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember_1591" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_OtherNoncurrentFinancialAssets_1596" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_TradeAndOtherPayables_1597" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_OtherCurrentFinancialLiabilities_1598" />
    <link:definitionArc xlink:type="arc" order="16.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_OtherNoncurrentFinancialLiabilities_1599" />
    <link:definitionArc xlink:type="arc" order="17.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="tsat_BorrowingsBeforeDeferredFinancingCosts_1600" />
    <link:definitionArc xlink:type="arc" order="18.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_NetAssetsLiabilities_1601" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="tsat_FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetailsTable_1579" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetailsTable_1579" xlink:to="ifrs-full_ClassesOfFinancialAssetsAxis_1580" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfFinancialAssetsAxis_1580" xlink:to="ifrs-full_ClassesOfFinancialAssetsDomain_1581" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetailsTable_1579" xlink:to="ifrs-full_LevelsOfFairValueHierarchyAxis_1583" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_LevelsOfFairValueHierarchyAxis_1583" xlink:to="ifrs-full_LevelsOfFairValueHierarchyDomain_1584" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofFinancialAssetsandFinancialLiabilitiesDetailsTable_1579" xlink:to="ifrs-full_CategoriesOfFinancialAssetsAxis_1588" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_CategoriesOfFinancialAssetsAxis_1588" xlink:to="ifrs-full_CategoriesOfFinancialAssetsDomain_1589" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_CashAndCashEquivalents_1593" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_TradeAndOtherReceivables_1594" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValuesOfItemsUsedAsDeemedCostLineItems_1592" xlink:to="ifrs-full_OtherCurrentFinancialAssets_1595" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfFinancialAssetsAxis_1580" xlink:to="ifrs-full_ClassesOfFinancialAssetsDomain_1581_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_LevelsOfFairValueHierarchyAxis_1583" xlink:to="ifrs-full_LevelsOfFairValueHierarchyDomain_1584_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_CategoriesOfFinancialAssetsAxis_1588" xlink:to="ifrs-full_CategoriesOfFinancialAssetsDomain_1589_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofPercentageofFaceValueoftheIndebtednessDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandAndTwentySixSeniorSecuredNotesMember" xlink:label="tsat_TwoThousandAndTwentySixSeniorSecuredNotesMember_1609" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatLightspeedFinancingMember" xlink:label="tsat_TelesatLightspeedFinancingMember_1610" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TermLoanBUSFacilityMember" xlink:label="tsat_TermLoanBUSFacilityMember_1606" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandAndTwentySevenSeniorUnsecuredNotesMember" xlink:label="tsat_TwoThousandAndTwentySevenSeniorUnsecuredNotesMember_1607" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TowThousandAndTwentySevenSeniorSecuredNotesMember" xlink:label="tsat_TowThousandAndTwentySevenSeniorSecuredNotesMember_1608" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfSignificantUnobservableInputsUsedInFairValueMeasurementOfEquityLineItems" xlink:label="ifrs-full_DisclosureOfSignificantUnobservableInputsUsedInFairValueMeasurementOfEquityLineItems_1611" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_Percentageoffairvalueindebtedness" xlink:label="tsat_Percentageoffairvalueindebtedness_1612" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain" xlink:label="ifrs-full_BorrowingsByNameDomain_1907" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinancialInstrumentsScheduleofPercentageofFaceValueoftheIndebtednessDetailsTable" xlink:label="tsat_FinancialInstrumentsScheduleofPercentageofFaceValueoftheIndebtednessDetailsTable_1604" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameAxis" xlink:label="ifrs-full_BorrowingsByNameAxis_1605" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_BorrowingsByNameDomain" xlink:label="ifrs-full_BorrowingsByNameDomain_1907_default" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1907" xlink:to="tsat_TwoThousandAndTwentySixSeniorSecuredNotesMember_1609" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1907" xlink:to="tsat_TelesatLightspeedFinancingMember_1610" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1907" xlink:to="tsat_TermLoanBUSFacilityMember_1606" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1907" xlink:to="tsat_TwoThousandAndTwentySevenSeniorUnsecuredNotesMember_1607" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_BorrowingsByNameDomain_1907" xlink:to="tsat_TowThousandAndTwentySevenSeniorSecuredNotesMember_1608" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfSignificantUnobservableInputsUsedInFairValueMeasurementOfEquityLineItems_1611" xlink:to="tsat_Percentageoffairvalueindebtedness_1612" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_BorrowingsByNameAxis_1605" xlink:to="ifrs-full_BorrowingsByNameDomain_1907" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfSignificantUnobservableInputsUsedInFairValueMeasurementOfEquityLineItems_1611" xlink:to="tsat_FinancialInstrumentsScheduleofPercentageofFaceValueoftheIndebtednessDetailsTable_1604" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofPercentageofFaceValueoftheIndebtednessDetailsTable_1604" xlink:to="ifrs-full_BorrowingsByNameAxis_1605" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_BorrowingsByNameAxis_1605" xlink:to="ifrs-full_BorrowingsByNameDomain_1907_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofValueoftheTelesatFinancingWarrantsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentOfCanadaMember" xlink:label="tsat_GovernmentOfCanadaMember_1618" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentOfQuebecMember" xlink:label="tsat_GovernmentOfQuebecMember_1619" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NoncurrentDerivativeFinancialLiabilities" xlink:label="ifrs-full_NoncurrentDerivativeFinancialLiabilities_1621" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ChangeInFairValueOfFinancingWarrants" xlink:label="tsat_ChangeInFairValueOfFinancingWarrants_1622" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NetForeignExchangeLoss" xlink:label="ifrs-full_NetForeignExchangeLoss_1623" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinancialInstrumentsScheduleofMovementsinTelesatLightspeedFinancingWarrantsDetailsTable" xlink:label="tsat_FinancialInstrumentsScheduleofMovementsinTelesatLightspeedFinancingWarrantsDetailsTable_1615" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_WarrantsAxis" xlink:label="tsat_WarrantsAxis_1616" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_WarrantsDomainDomain" xlink:label="tsat_WarrantsDomainDomain_1617" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ScheduleOfMovementsInTelesatLightspeedFinancingWarrantsLineItems" xlink:label="tsat_ScheduleOfMovementsInTelesatLightspeedFinancingWarrantsLineItems_1620" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_WarrantsDomainDomain" xlink:label="tsat_WarrantsDomainDomain_1617_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_WarrantsDomainDomain_1617" xlink:to="tsat_GovernmentOfCanadaMember_1618" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_WarrantsDomainDomain_1617" xlink:to="tsat_GovernmentOfQuebecMember_1619" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfMovementsInTelesatLightspeedFinancingWarrantsLineItems_1620" xlink:to="ifrs-full_NoncurrentDerivativeFinancialLiabilities_1621" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfMovementsInTelesatLightspeedFinancingWarrantsLineItems_1620" xlink:to="tsat_ChangeInFairValueOfFinancingWarrants_1622" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_ScheduleOfMovementsInTelesatLightspeedFinancingWarrantsLineItems_1620" xlink:to="ifrs-full_NetForeignExchangeLoss_1623" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_ScheduleOfMovementsInTelesatLightspeedFinancingWarrantsLineItems_1620" xlink:to="tsat_FinancialInstrumentsScheduleofMovementsinTelesatLightspeedFinancingWarrantsDetailsTable_1615" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofMovementsinTelesatLightspeedFinancingWarrantsDetailsTable_1615" xlink:to="tsat_WarrantsAxis_1616" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="tsat_WarrantsAxis_1616" xlink:to="tsat_WarrantsDomainDomain_1617" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="tsat_WarrantsAxis_1616" xlink:to="tsat_WarrantsDomainDomain_1617_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/EmployeeBenefitPlansScheduleofExpensesIncludedontheCondensedConsolidatedStatementsofIncomeLossDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherPostemploymentBenefitPlansUSMember" xlink:label="tsat_OtherPostemploymentBenefitPlansUSMember_1633" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherPostemploymentBenefitPlansTotalMember" xlink:label="tsat_OtherPostemploymentBenefitPlansTotalMember_1634" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PensionPlansCanadianMember" xlink:label="tsat_PensionPlansCanadianMember_1629" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PensionPlansUSMember" xlink:label="tsat_PensionPlansUSMember_1630" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PensionPlansTotalMember" xlink:label="tsat_PensionPlansTotalMember_1631" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherPostemploymentBenefitPlansCanadianMember" xlink:label="tsat_OtherPostemploymentBenefitPlansCanadianMember_1632" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemLineItems" xlink:label="ifrs-full_DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemLineItems_1635" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OperatingExpense" xlink:label="ifrs-full_OperatingExpense_1636" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestRevenueExpense" xlink:label="ifrs-full_InterestRevenueExpense_1637" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DefinedBenefitPlansDomain" xlink:label="ifrs-full_DefinedBenefitPlansDomain_1908" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_EmployeeBenefitPlansScheduleofExpensesIncludedontheCondensedConsolidatedStatementsofIncomeLossDetailsTable" xlink:label="tsat_EmployeeBenefitPlansScheduleofExpensesIncludedontheCondensedConsolidatedStatementsofIncomeLossDetailsTable_1627" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DefinedBenefitPlansAxis" xlink:label="ifrs-full_DefinedBenefitPlansAxis_1628" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DefinedBenefitPlansDomain" xlink:label="ifrs-full_DefinedBenefitPlansDomain_1908_default" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1908" xlink:to="tsat_OtherPostemploymentBenefitPlansUSMember_1633" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1908" xlink:to="tsat_OtherPostemploymentBenefitPlansTotalMember_1634" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1908" xlink:to="tsat_PensionPlansCanadianMember_1629" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1908" xlink:to="tsat_PensionPlansUSMember_1630" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1908" xlink:to="tsat_PensionPlansTotalMember_1631" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1908" xlink:to="tsat_OtherPostemploymentBenefitPlansCanadianMember_1632" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemLineItems_1635" xlink:to="ifrs-full_OperatingExpense_1636" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemLineItems_1635" xlink:to="ifrs-full_InterestRevenueExpense_1637" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_DefinedBenefitPlansAxis_1628" xlink:to="ifrs-full_DefinedBenefitPlansDomain_1908" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemLineItems_1635" xlink:to="tsat_EmployeeBenefitPlansScheduleofExpensesIncludedontheCondensedConsolidatedStatementsofIncomeLossDetailsTable_1627" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_EmployeeBenefitPlansScheduleofExpensesIncludedontheCondensedConsolidatedStatementsofIncomeLossDetailsTable_1627" xlink:to="ifrs-full_DefinedBenefitPlansAxis_1628" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_DefinedBenefitPlansAxis_1628" xlink:to="ifrs-full_DefinedBenefitPlansDomain_1908_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/FinancialInstrumentsScheduleofInterestPayableandInterestPaymentsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SatellitePerformanceIncentivePaymentsMember" xlink:label="tsat_SatellitePerformanceIncentivePaymentsMember_1572" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessMember" xlink:label="tsat_IndebtednessMember_1573" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_FinancialInstrumentsScheduleofInterestPayableandInterestPaymentsDetailsTable" xlink:label="tsat_FinancialInstrumentsScheduleofInterestPayableandInterestPaymentsDetailsTable_1570" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain" xlink:label="ifrs-full_ClassesOfFinancialInstrumentsDomain_1906" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsAxis" xlink:label="ifrs-full_ClassesOfFinancialInstrumentsAxis_1571" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems" xlink:label="ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_1574" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_InterestPayable" xlink:label="ifrs-full_InterestPayable_1575" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_InterestPayments" xlink:label="tsat_InterestPayments_1576" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain" xlink:label="ifrs-full_ClassesOfFinancialInstrumentsDomain_1906_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsDomain_1906" xlink:to="tsat_SatellitePerformanceIncentivePaymentsMember_1572" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsDomain_1906" xlink:to="tsat_IndebtednessMember_1573" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_1574" xlink:to="tsat_FinancialInstrumentsScheduleofInterestPayableandInterestPaymentsDetailsTable_1570" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsAxis_1571" xlink:to="ifrs-full_ClassesOfFinancialInstrumentsDomain_1906" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_FinancialInstrumentsScheduleofInterestPayableandInterestPaymentsDetailsTable_1570" xlink:to="ifrs-full_ClassesOfFinancialInstrumentsAxis_1571" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_1574" xlink:to="ifrs-full_InterestPayable_1575" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfMaturityAnalysisForDerivativeFinancialLiabilitiesLineItems_1574" xlink:to="tsat_InterestPayments_1576" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsAxis_1571" xlink:to="ifrs-full_ClassesOfFinancialInstrumentsDomain_1906_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/EmployeeBenefitPlansScheduleofBalanceSheetObligationsDistributedBetweenPensionandOtherPostEmploymentBenefitsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PensionPlansTotalMember" xlink:label="tsat_PensionPlansTotalMember_1644" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherPostemploymentBenefitPlansCanadianMember" xlink:label="tsat_OtherPostemploymentBenefitPlansCanadianMember_1645" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherPostemploymentBenefitPlansUSMember" xlink:label="tsat_OtherPostemploymentBenefitPlansUSMember_1646" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OtherPostemploymentBenefitPlansTotalMember" xlink:label="tsat_OtherPostemploymentBenefitPlansTotalMember_1647" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PensionPlansCanadianMember" xlink:label="tsat_PensionPlansCanadianMember_1642" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PensionPlansUSMember" xlink:label="tsat_PensionPlansUSMember_1643" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DefinedBenefitPlansDomain" xlink:label="ifrs-full_DefinedBenefitPlansDomain_1909" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfFairValueOfPlanAssetsLineItems" xlink:label="ifrs-full_DisclosureOfFairValueOfPlanAssetsLineItems_1648" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_EmployeeBenefitPlansScheduleofBalanceSheetObligationsDistributedBetweenPensionandOtherPostEmploymentBenefitsDetailsTable" xlink:label="tsat_EmployeeBenefitPlansScheduleofBalanceSheetObligationsDistributedBetweenPensionandOtherPostEmploymentBenefitsDetailsTable_1640" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DefinedBenefitPlansAxis" xlink:label="ifrs-full_DefinedBenefitPlansAxis_1641" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherNoncurrentFinancialLiabilities" xlink:label="ifrs-full_OtherNoncurrentFinancialLiabilities_1649" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherNoncurrentAssets" xlink:label="ifrs-full_OtherNoncurrentAssets_1651" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DefinedBenefitPlansDomain" xlink:label="ifrs-full_DefinedBenefitPlansDomain_1909_default" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1909" xlink:to="tsat_PensionPlansTotalMember_1644" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1909" xlink:to="tsat_OtherPostemploymentBenefitPlansCanadianMember_1645" />
    <link:definitionArc xlink:type="arc" order="14.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1909" xlink:to="tsat_OtherPostemploymentBenefitPlansUSMember_1646" />
    <link:definitionArc xlink:type="arc" order="15.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1909" xlink:to="tsat_OtherPostemploymentBenefitPlansTotalMember_1647" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1909" xlink:to="tsat_PensionPlansCanadianMember_1642" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DefinedBenefitPlansDomain_1909" xlink:to="tsat_PensionPlansUSMember_1643" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_DefinedBenefitPlansAxis_1641" xlink:to="ifrs-full_DefinedBenefitPlansDomain_1909" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfFairValueOfPlanAssetsLineItems_1648" xlink:to="tsat_EmployeeBenefitPlansScheduleofBalanceSheetObligationsDistributedBetweenPensionandOtherPostEmploymentBenefitsDetailsTable_1640" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_EmployeeBenefitPlansScheduleofBalanceSheetObligationsDistributedBetweenPensionandOtherPostEmploymentBenefitsDetailsTable_1640" xlink:to="ifrs-full_DefinedBenefitPlansAxis_1641" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValueOfPlanAssetsLineItems_1648" xlink:to="ifrs-full_OtherNoncurrentFinancialLiabilities_1649" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfFairValueOfPlanAssetsLineItems_1648" xlink:to="ifrs-full_OtherNoncurrentAssets_1651" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_DefinedBenefitPlansAxis_1641" xlink:to="ifrs-full_DefinedBenefitPlansDomain_1909_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/EventsAftertheReportingPeriodDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ForecastMember" xlink:label="tsat_ForecastMember_1970" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable" xlink:label="ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_1966" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodAxis" xlink:label="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1967" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodDomain" xlink:label="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1968" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems" xlink:label="ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_1969" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherBorrowings" xlink:label="ifrs-full_OtherBorrowings_1971" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NonadjustingEventsAfterReportingPeriodDomain" xlink:label="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1968_default" />
    <link:definitionArc xlink:type="arc" order="58.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1968" xlink:to="tsat_ForecastMember_1970" />
    <link:definitionArc xlink:type="arc" order="54.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_1969" xlink:to="ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_1966" />
    <link:definitionArc xlink:type="arc" order="55.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodTable_1966" xlink:to="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1967" />
    <link:definitionArc xlink:type="arc" order="56.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1967" xlink:to="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1968" />
    <link:definitionArc xlink:type="arc" order="59.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems_1969" xlink:to="ifrs-full_OtherBorrowings_1971" />
    <link:definitionArc xlink:type="arc" order="56.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_NonadjustingEventsAfterReportingPeriodAxis_1967" xlink:to="ifrs-full_NonadjustingEventsAfterReportingPeriodDomain_1968_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/IndebtednessScheduleofIndebtednessParentheticalsDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TermLoanBUSFacilityMember" xlink:label="tsat_TermLoanBUSFacilityMember_1411" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember" xlink:label="tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember_1412" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySixSeniorSecuredNotesMember" xlink:label="tsat_TwoThousandTwentySixSeniorSecuredNotesMember_1413" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TwoThousandTwentySevenSeniorSecuredNotesMember" xlink:label="tsat_TwoThousandTwentySevenSeniorSecuredNotesMember_1414" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessScheduleofIndebtednessParentheticalsDetailsTable" xlink:label="tsat_IndebtednessScheduleofIndebtednessParentheticalsDetailsTable_1409" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsAxis" xlink:label="tsat_DebtInstrumentsAxis_1410" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfCreditRiskExposureLineItems" xlink:label="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1415" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PaymentOfTermLoan" xlink:label="tsat_PaymentOfTermLoan_1416" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SeniorNotesAmount" xlink:label="tsat_SeniorNotesAmount_1417" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_PaymentsOfOptionsSeniorSecuredNotes" xlink:label="tsat_PaymentsOfOptionsSeniorSecuredNotes_1418" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsDomainDomain" xlink:label="tsat_DebtInstrumentsDomainDomain_1900" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtInstrumentsDomainDomain" xlink:label="tsat_DebtInstrumentsDomainDomain_1900_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1900" xlink:to="tsat_TermLoanBUSFacilityMember_1411" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1900" xlink:to="tsat_TwoThousandTwentySevenSeniorUnsecuredNotesMember_1412" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1900" xlink:to="tsat_TwoThousandTwentySixSeniorSecuredNotesMember_1413" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DebtInstrumentsDomainDomain_1900" xlink:to="tsat_TwoThousandTwentySevenSeniorSecuredNotesMember_1414" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1415" xlink:to="tsat_IndebtednessScheduleofIndebtednessParentheticalsDetailsTable_1409" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_IndebtednessScheduleofIndebtednessParentheticalsDetailsTable_1409" xlink:to="tsat_DebtInstrumentsAxis_1410" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1415" xlink:to="tsat_PaymentOfTermLoan_1416" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1415" xlink:to="tsat_SeniorNotesAmount_1417" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfCreditRiskExposureLineItems_1415" xlink:to="tsat_PaymentsOfOptionsSeniorSecuredNotes_1418" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="tsat_DebtInstrumentsAxis_1410" xlink:to="tsat_DebtInstrumentsDomainDomain_1900" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="tsat_DebtInstrumentsAxis_1410" xlink:to="tsat_DebtInstrumentsDomainDomain_1900_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/IndebtednessScheduleofActivityinDeferredFinancingChargesDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatLightspeedFinancingWarrantsMember" xlink:label="tsat_TelesatLightspeedFinancingWarrantsMember_1423" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DebtIssueCostsMember" xlink:label="tsat_DebtIssueCostsMember_1424" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TotalDeferredFinancingChargesMember" xlink:label="tsat_TotalDeferredFinancingChargesMember_1425" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_IndebtednessScheduleofActivityinDeferredFinancingChargesDetailsTable" xlink:label="tsat_IndebtednessScheduleofActivityinDeferredFinancingChargesDetailsTable_1421" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesAxis" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1422" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredFinancingChargesLineItems" xlink:label="tsat_DeferredFinancingChargesLineItems_1426" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1901" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_DeferredFinancingChargesBalance" xlink:label="tsat_DeferredFinancingChargesBalance_1427" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TransferredToDebtIssueCosts" xlink:label="tsat_TransferredToDebtIssueCosts_1429" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ForeignExchange" xlink:label="tsat_ForeignExchange_1430" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialLiabilitiesDomain" xlink:label="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1901_default" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1901" xlink:to="tsat_TelesatLightspeedFinancingWarrantsMember_1423" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1901" xlink:to="tsat_DebtIssueCostsMember_1424" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1901" xlink:to="tsat_TotalDeferredFinancingChargesMember_1425" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_DeferredFinancingChargesLineItems_1426" xlink:to="tsat_IndebtednessScheduleofActivityinDeferredFinancingChargesDetailsTable_1421" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_IndebtednessScheduleofActivityinDeferredFinancingChargesDetailsTable_1421" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1422" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1422" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1901" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DeferredFinancingChargesLineItems_1426" xlink:to="tsat_DeferredFinancingChargesBalance_1427" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DeferredFinancingChargesLineItems_1426" xlink:to="tsat_TransferredToDebtIssueCosts_1429" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_DeferredFinancingChargesLineItems_1426" xlink:to="tsat_ForeignExchange_1430" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfFinancialLiabilitiesAxis_1422" xlink:to="ifrs-full_ClassesOfFinancialLiabilitiesDomain_1901_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails1" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatPublicSharesMember" xlink:label="tsat_TelesatPublicSharesMember_1436" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassCCommonSharesMember" xlink:label="tsat_ClassCCommonSharesMember_1437" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable" xlink:label="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1433" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis" xlink:label="ifrs-full_ClassesOfShareCapitalAxis_1434" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NumberOfSharesOutstanding" xlink:label="ifrs-full_NumberOfSharesOutstanding_1439" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_IssuedCapital" xlink:label="ifrs-full_IssuedCapital_1440" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1435" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfClassesOfShareCapitalLineItems" xlink:label="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1438" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1435_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1435" xlink:to="tsat_TelesatPublicSharesMember_1436" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1435" xlink:to="tsat_ClassCCommonSharesMember_1437" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1438" xlink:to="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1433" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1433" xlink:to="ifrs-full_ClassesOfShareCapitalAxis_1434" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1438" xlink:to="ifrs-full_NumberOfSharesOutstanding_1439" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1438" xlink:to="ifrs-full_IssuedCapital_1440" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1434" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1435" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1434" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1435_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/NonControllingInterestDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_NoncontrollingInterestsMember" xlink:label="ifrs-full_NoncontrollingInterestsMember_1819" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NonControllingInterestLineItems" xlink:label="tsat_NonControllingInterestLineItems_1820" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ProportionOfOwnershipInterestsHeldByNoncontrollingInterests" xlink:label="ifrs-full_ProportionOfOwnershipInterestsHeldByNoncontrollingInterests_1821" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NonControllingInterestDetailsTable" xlink:label="tsat_NonControllingInterestDetailsTable_1816" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityAxis" xlink:label="ifrs-full_ComponentsOfEquityAxis_1817" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain" xlink:label="ifrs-full_ComponentsOfEquityDomain_1818" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ComponentsOfEquityDomain" xlink:label="ifrs-full_ComponentsOfEquityDomain_1818_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ComponentsOfEquityDomain_1818" xlink:to="ifrs-full_NoncontrollingInterestsMember_1819" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_NonControllingInterestLineItems_1820" xlink:to="ifrs-full_ProportionOfOwnershipInterestsHeldByNoncontrollingInterests_1821" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_NonControllingInterestLineItems_1820" xlink:to="tsat_NonControllingInterestDetailsTable_1816" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_NonControllingInterestDetailsTable_1816" xlink:to="ifrs-full_ComponentsOfEquityAxis_1817" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ComponentsOfEquityAxis_1817" xlink:to="ifrs-full_ComponentsOfEquityDomain_1818" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ComponentsOfEquityAxis_1817" xlink:to="ifrs-full_ComponentsOfEquityDomain_1818_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetails2" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassACommonSharesMember" xlink:label="tsat_ClassACommonSharesMember_1446" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ClassBVariableVotingSharesMember" xlink:label="tsat_ClassBVariableVotingSharesMember_1447" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable" xlink:label="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1443" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalAxis" xlink:label="ifrs-full_ClassesOfShareCapitalAxis_1444" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1445" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_DisclosureOfClassesOfShareCapitalLineItems" xlink:label="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1448" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_TelesatPublicSharesAbstract" xlink:label="tsat_TelesatPublicSharesAbstract_1449" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_BreakDownOfTelesatPublicShares" xlink:label="tsat_BreakDownOfTelesatPublicShares_1450" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfShareCapitalDomain" xlink:label="ifrs-full_ClassesOfShareCapitalDomain_1445_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1445" xlink:to="tsat_ClassACommonSharesMember_1446" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfShareCapitalDomain_1445" xlink:to="tsat_ClassBVariableVotingSharesMember_1447" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1448" xlink:to="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1443" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_ShareCapitalScheduleofNumberofSharesandStatedValueoftheOutstandingSharesDetailsTable_1443" xlink:to="ifrs-full_ClassesOfShareCapitalAxis_1444" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1444" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1445" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_DisclosureOfClassesOfShareCapitalLineItems_1448" xlink:to="tsat_TelesatPublicSharesAbstract_1449" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_TelesatPublicSharesAbstract_1449" xlink:to="tsat_BreakDownOfTelesatPublicShares_1450" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfShareCapitalAxis_1444" xlink:to="ifrs-full_ClassesOfShareCapitalDomain_1445_default" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://telesat.com/20260630/role/GovernmentGrantDetails" xlink:type="extended" xlink:title="definitionLink">
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_SatellitesPropertyAndOtherEquipmentMember" xlink:label="tsat_SatellitesPropertyAndOtherEquipmentMember_1834" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_OperatingExpensesMember" xlink:label="tsat_OperatingExpensesMember_1835" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentGrantDetailsTable" xlink:label="tsat_GovernmentGrantDetailsTable_1831" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsAxis" xlink:label="ifrs-full_ClassesOfFinancialInstrumentsAxis_1832" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain" xlink:label="ifrs-full_ClassesOfFinancialInstrumentsDomain_1833" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ReductionOfIssuedCapital" xlink:label="ifrs-full_ReductionOfIssuedCapital_1839" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_OtherPropertyPlantAndEquipment" xlink:label="ifrs-full_OtherPropertyPlantAndEquipment_1840" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_GovernmentGrantLineItems" xlink:label="tsat_GovernmentGrantLineItems_1836" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_NonrefundableGovernmentContributionValue" xlink:label="tsat_NonrefundableGovernmentContributionValue_1837" />
    <link:loc xlink:type="locator" xlink:href="tsat-20260630.xsd#tsat_RecordedRelatingToAgreement" xlink:label="tsat_RecordedRelatingToAgreement_1838" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.ifrs.org/taxonomy/2025-03-27/full_ifrs/full_ifrs-cor_2025-03-27.xsd#ifrs-full_ClassesOfFinancialInstrumentsDomain" xlink:label="ifrs-full_ClassesOfFinancialInstrumentsDomain_1833_default" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsDomain_1833" xlink:to="tsat_SatellitesPropertyAndOtherEquipmentMember_1834" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsDomain_1833" xlink:to="tsat_OperatingExpensesMember_1835" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="true" use="optional" xbrldt:contextElement="segment" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="tsat_GovernmentGrantLineItems_1836" xlink:to="tsat_GovernmentGrantDetailsTable_1831" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="tsat_GovernmentGrantDetailsTable_1831" xlink:to="ifrs-full_ClassesOfFinancialInstrumentsAxis_1832" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsAxis_1832" xlink:to="ifrs-full_ClassesOfFinancialInstrumentsDomain_1833" />
    <link:definitionArc xlink:type="arc" order="12.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_GovernmentGrantLineItems_1836" xlink:to="ifrs-full_ReductionOfIssuedCapital_1839" />
    <link:definitionArc xlink:type="arc" order="13.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_GovernmentGrantLineItems_1836" xlink:to="ifrs-full_OtherPropertyPlantAndEquipment_1840" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_GovernmentGrantLineItems_1836" xlink:to="tsat_NonrefundableGovernmentContributionValue_1837" />
    <link:definitionArc xlink:type="arc" order="11.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="tsat_GovernmentGrantLineItems_1836" xlink:to="tsat_RecordedRelatingToAgreement_1838" />
    <link:definitionArc xlink:type="arc" order="10.00000" priority="1" xbrldt:closed="false" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ifrs-full_ClassesOfFinancialInstrumentsAxis_1832" xlink:to="ifrs-full_ClassesOfFinancialInstrumentsDomain_1833_default" />
  </link:definitionLink>
</link:linkbase>
