<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:c6b5746e-9991-467d-93ce-2ea7a88121f2,g:2781fb58-eaba-4de7-bc54-b9130cc47d42-->
<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:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://ucbi.com/role/CoverPage" xlink:type="simple" xlink:href="ucbi-20251208.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://ucbi.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityListingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsTable_3b53a9df-1d24-4e4b-840f-a677dbe84229" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityListingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityListingsTable_3b53a9df-1d24-4e4b-840f-a677dbe84229" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_2e98a116-ec88-4bb7-a6af-f8c4b5894f1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntityListingsTable_3b53a9df-1d24-4e4b-840f-a677dbe84229" xlink:to="loc_us-gaap_StatementClassOfStockAxis_2e98a116-ec88-4bb7-a6af-f8c4b5894f1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_2e98a116-ec88-4bb7-a6af-f8c4b5894f1b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_2e98a116-ec88-4bb7-a6af-f8c4b5894f1b" xlink:to="loc_us-gaap_ClassOfStockDomain_2e98a116-ec88-4bb7-a6af-f8c4b5894f1b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0f483279-9b7c-43b4-b809-fa23f56159cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_2e98a116-ec88-4bb7-a6af-f8c4b5894f1b" xlink:to="loc_us-gaap_ClassOfStockDomain_0f483279-9b7c-43b4-b809-fa23f56159cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_b46402b4-32cb-493c-8dcd-ef498ba0369a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0f483279-9b7c-43b4-b809-fa23f56159cc" xlink:to="loc_us-gaap_CommonStockMember_b46402b4-32cb-493c-8dcd-ef498ba0369a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ucbi_UCBISeriesINonCumulativePreferredStockMember_3edc6f72-c859-48c5-8863-14bffc3d07b2" xlink:href="ucbi-20251208.xsd#ucbi_UCBISeriesINonCumulativePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0f483279-9b7c-43b4-b809-fa23f56159cc" xlink:to="loc_ucbi_UCBISeriesINonCumulativePreferredStockMember_3edc6f72-c859-48c5-8863-14bffc3d07b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_afef9b7c-ec7d-49e5-a4f7-80f32bf17743" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_DocumentType_afef9b7c-ec7d-49e5-a4f7-80f32bf17743" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_902a7d5e-28ac-415d-a53b-81770dc97b0f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_DocumentPeriodEndDate_902a7d5e-28ac-415d-a53b-81770dc97b0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_029d8a64-d1d6-4fe1-a279-e9ea0e1f6fe4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityRegistrantName_029d8a64-d1d6-4fe1-a279-e9ea0e1f6fe4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_97d2f5e7-d897-424d-9b54-21069aa12461" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityCentralIndexKey_97d2f5e7-d897-424d-9b54-21069aa12461" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_5397e53e-7561-4da3-a38b-bc7255af3a75" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_AmendmentFlag_5397e53e-7561-4da3-a38b-bc7255af3a75" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_6aab8c0a-1426-48ad-8914-140a00513a78" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityIncorporationStateCountryCode_6aab8c0a-1426-48ad-8914-140a00513a78" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_d956ff29-776d-4cf0-a154-fb7f9139bcfe" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityFileNumber_d956ff29-776d-4cf0-a154-fb7f9139bcfe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_57d4f1dd-1ac1-486f-92fb-85fb71f7c784" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityTaxIdentificationNumber_57d4f1dd-1ac1-486f-92fb-85fb71f7c784" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_77fa5b8e-a4d0-4dcb-b957-2718e8810099" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityAddressAddressLine1_77fa5b8e-a4d0-4dcb-b957-2718e8810099" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_c9c32fb8-fd77-41db-b46c-b333c62b62c1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityAddressCityOrTown_c9c32fb8-fd77-41db-b46c-b333c62b62c1" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_f21e8c2b-d906-4f19-895d-8bccb603516d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityAddressStateOrProvince_f21e8c2b-d906-4f19-895d-8bccb603516d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_477fbd42-09e9-4596-8e6d-bc4221d0cd15" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityAddressPostalZipCode_477fbd42-09e9-4596-8e6d-bc4221d0cd15" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_dcc3bb8f-be50-4367-b628-cf95ed7f1dce" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_CityAreaCode_dcc3bb8f-be50-4367-b628-cf95ed7f1dce" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_a883bb29-96e4-4458-aba2-ee15db90ad31" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_LocalPhoneNumber_a883bb29-96e4-4458-aba2-ee15db90ad31" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_cf969920-85f5-49c1-b1a5-647e2735c508" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_WrittenCommunications_cf969920-85f5-49c1-b1a5-647e2735c508" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_e75b8462-7c9e-4f11-bd93-11bb4728ce08" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_SolicitingMaterial_e75b8462-7c9e-4f11-bd93-11bb4728ce08" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_1b386454-0d9c-4f75-8ddc-dcaac0bf7a7f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_PreCommencementTenderOffer_1b386454-0d9c-4f75-8ddc-dcaac0bf7a7f" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_3985e09d-7a7e-4a1c-bebb-55f474b9ff35" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_3985e09d-7a7e-4a1c-bebb-55f474b9ff35" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_f19b4a38-dc13-4a08-8e79-07be887b2628" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_Security12bTitle_f19b4a38-dc13-4a08-8e79-07be887b2628" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_75b00f4e-9a6f-4aad-8361-486632f9874f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_TradingSymbol_75b00f4e-9a6f-4aad-8361-486632f9874f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_3726b60c-f613-4954-838c-2bdfa08d6dd9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_SecurityExchangeName_3726b60c-f613-4954-838c-2bdfa08d6dd9" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_ca17e0d2-69d9-4b30-a90c-7322d63a1f54" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityListingsLineItems_1b55df67-37e8-43fa-989c-e7de31b31f3e" xlink:to="loc_dei_EntityEmergingGrowthCompany_ca17e0d2-69d9-4b30-a90c-7322d63a1f54" xlink:type="arc" order="21"/>
  </link:definitionLink>
</link:linkbase>
