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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2020-03-31</periodOfReport>

    <dateOfOriginalSubmission>2020-09-17</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001810806</issuerCik>
        <issuerName>Unity Software Inc.</issuerName>
        <issuerTradingSymbol>U</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001222287</rptOwnerCik>
            <rptOwnerName>BOTHA ROELOF</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2800 SAND HILL ROAD, SUITE 101</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MENLO PARK</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Series E Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F4"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-03-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3719996</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3719996</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4351309</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Sequoia Capital Global Growth Fund III - Endurance Partners, L.P.</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This amendment is being filed solely to correct the transaction code in column 4 of Table II from code &quot;A&quot; to code &quot;P&quot; and to move the number of derivative securities acquired or disposed of in column 5 of Table II from the &quot;D&quot; column to the &quot;A&quot; column.  Other than the above-referenced corrections, the original Form 4 filing remains unchanged.</footnote>
        <footnote id="F2">The Reporting Person is a director and stockholder of SC US (TTGP), Ltd. SC US (TTGP), Ltd. is (i) the general partner of SC U.S. Growth VI Management, L.P., which is the general partner of each of Sequoia Capital U.S. Growth Fund VI, L.P. (GFVI) and Sequoia Capital U.S. Growth VI Principals Fund, L.P. (GFVI PF) (collectively, the GFVI Funds); (ii) the general partner of SCGGF Management, L.P., which is the general partner of each of Sequoia Capital Global Growth Fund, LP (GGF) and Sequoia Capital Global Growth Principals Fund, LP (GGF PF) (collectively, the GGF Funds); and (iii) the general partner of SCGGF III - Endurance Partners Management, L.P., which is the general partner of Sequoia Capital Global Growth Fund III - Endurance Partners, L.P. (GGF III).</footnote>
        <footnote id="F3">(continued from footnote 2) Voting and disposition decisions at SC US (TTGP), Ltd. with respect to the shares held by the GGF III are made by an investment committee that includes the Reporting Person. The Reporting Person disclaims beneficial ownership of the securities included in this report, except to the extent of his pecuniary interest therein, and the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of the reported securities for purposes of Section 16 or for any other purposes.</footnote>
        <footnote id="F4">The Series E Preferred Stock is convertible into shares of common stock on a 1:1 basis and has no expiration date. Immediately prior to the consummation of the Issuer's initial public offering, all shares of Series E Preferred Stock will automatically convert into shares of common stock of the Issuer.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Jung Yeon Son, Attorney-in-fact for Roelof Botha</signatureName>
        <signatureDate>2020-09-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
