<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0609</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-05-07</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001745431</issuerCik>
        <issuerName>StoneCo Ltd.</issuerName>
        <issuerTradingSymbol>STNE</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002085762</rptOwnerCik>
            <rptOwnerName>Fresco Gutierrez Diego</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>true</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>4TH FLOOR, HARBOUR PLACE</rptOwnerStreet1>
            <rptOwnerStreet2>103 SOUTH CHURCH STREET, P.O. BOX 10240</rptOwnerStreet2>
            <rptOwnerCity>GRAND CAYMAN</rptOwnerCity>
            <rptOwnerNonUSStateTerritory>CAYMAN ISLANDS</rptOwnerNonUSStateTerritory>
            <rptOwnerCountry>E9</rptOwnerCountry>
            <rptOwnerZipCode>KY1-1002</rptOwnerZipCode>
            <rptOwnerStateDescription>CAYMAN ISLANDS</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-05-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3869</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24680</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents the acquisition of dividend equivalent rights in the form of additional restricted stock units, which were credited in connection with the Issuer's dividend payment on previously granted restricted stock units awards. These additional restricted stock units are subject to the same terms and conditions, including vesting, as the underlying restricted stock units awards to which they relate.</footnote>
        <footnote id="F2">The additional restricted stock units were credited at no cash cost to the reporting person as a dividend equivalent on outstanding restricted stock units.</footnote>
        <footnote id="F3">Includes both restricted stock units that represent a contingent right to receive one share of the Issuer's Common Stock, as well as shares of Common Stock.</footnote>
    </footnotes>

    <remarks>Exhibit 24 - Power of Attorney</remarks>

    <ownerSignature>
        <signatureName>/s/Priscilla Saraiva Godoy, attorney-in-fact for Diego Fresco Gutierrez</signatureName>
        <signatureDate>2026-05-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
