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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2021-03-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001651052</issuerCik>
        <issuerName>Focus Financial Partners Inc.</issuerName>
        <issuerTradingSymbol>FOCS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001490137</rptOwnerCik>
            <rptOwnerName>Carey James D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O STONE POINT CAPITAL LLC</rptOwnerStreet1>
            <rptOwnerStreet2>20 HORSENECK LANE</rptOwnerStreet2>
            <rptOwnerCity>GREENWICH</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06830-6327</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-03-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1296885</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12793086</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F6"/>
                    <footnoteId id="F8"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-03-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4662270</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>46.20</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8130816</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F7"/>
                    <footnoteId id="F8"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Units of Focus Financial Partners, LLC</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2021-03-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1296885</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1296885</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8601385</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F5"/>
                    <footnoteId id="F8"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Units of Focus Financial Partners, LLC represent limited liability company units of Focus Financial Partners, LLC and an equal number of shares of Class B common stock (&quot;Class B Common Stock&quot;) of Focus Financial Partners Inc. (the &quot;Issuer&quot;), which together are exchangeable, at the option of Focus Financial Partners, LLC or the Issuer, on a one-for-one basis for (i) a share of Class A Common Stock (&quot;Class A Common Stock&quot;) of the Issuer, subject to conversion rate adjustments for stock splits, stock dividends, reclassification and other similar transactions or (ii) an equivalent amount of cash pursuant to the Fourth Amended and Restated Limited Liability Company Agreement of Focus Financial Partners, LLC.</footnote>
        <footnote id="F2">This amount represents the $48.00 secondary public offering price per share of Class A Common Stock less the underwriting discount of $1.80 per share of Class A Common Stock.</footnote>
        <footnote id="F3">Securities disposed of consists of shares of Class A Common Stock of the Issuer held as follows: (a) 2,396,693 shares of Class A Common Stock are held by Trident FFP LP, (b) 277,650 shares of Class A Common Stock are held by Trident VI, L.P., (c) 1,946,670 shares of Class A Common Stock are held by Trident VI Parallel Fund, L.P. and (d) 41,257 shares of Class A Common Stock are held by Trident VI DE Parallel Fund, L.P. The sole general partner of Trident FFP LP is Trident FFP GP LLC, and the sole general partner of each of Trident VI, L.P., Trident VI Parallel Fund, L.P. and Trident VI DE Parallel Fund, L.P. (collectively, the &quot;Trident VI Partnerships&quot; and, together with Trident FFP LP, the &quot;Trident Stockholders&quot;) is Trident Capital VI, L.P.</footnote>
        <footnote id="F4">Pursuant to certain management agreements, Stone Point Capital LLC has received delegated authority by Trident Capital VI, L.P. relating to the Trident VI Partnerships, provided that the delegated discretion to exercise voting rights may not be exercised on behalf of any of the Trident VI Partnerships without first receiving direction from the Investment Committee of Trident Capital VI, L.P. or a majority of the general partners of Trident Capital VI, L.P. The management agreements do not delegate any power with respect to the disposition of Class A Common Stock or Class B Common Stock held by the Trident VI Partnerships. James D. Carey, as a member and managing director at Stone Point Capital LLC and an owner of one of five members of Trident FFP GP LLC and one of five general partners of Trident Capital VI, L.P., may be deemed to be the beneficial owner of the securities held directly by the Trident Stockholders.</footnote>
        <footnote id="F5">Held by Trident FFP LP.</footnote>
        <footnote id="F6">Beneficially owned securities consists of shares of Class A Common Stock of the Issuer held as follows: (a) 2,396,693 shares of Class A Common Stock are held by Trident FFP LP, (b) 1,274,093 shares of Class A Common Stock are held by Trident VI, L.P., (c) 8,932,981 shares of Class A Common Stock are held by Trident VI Parallel Fund, L.P. and (d) 189,319 shares of Class A Common Stock are held by Trident VI DE Parallel Fund, L.P.</footnote>
        <footnote id="F7">Beneficially owned securities consists of shares of Class A Common Stock of the Issuer held as follows: (a) 0 shares of Class A Common Stock are held by Trident FFP LP, (b) 996,443 shares of Class A Common Stock are held by Trident VI, L.P., (c) 6,986,311 shares of Class A Common Stock are held by Trident VI Parallel Fund, L.P. and (d) 148,062 shares of Class A Common Stock are held by Trident VI DE Parallel Fund, L.P.</footnote>
        <footnote id="F8">Mr. Carey disclaims beneficial ownership of the shares and units held of record or beneficially by the Trident Stockholders, except to the extent of any pecuniary interest therein. The filing of this statement shall not be deemed to be an admission that, for purposes of Section 16 of the Securities and Exchange Act of 1934 or otherwise, Mr. Carey is the beneficial owner of any securities reported herein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ James D. Carey</signatureName>
        <signatureDate>2021-03-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
