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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-09-24</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001390478</issuerCik>
        <issuerName>SELLAS Life Sciences Group, Inc.</issuerName>
        <issuerTradingSymbol>SLS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724449</rptOwnerCik>
            <rptOwnerName>Lopez Fabio</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BERMUDIANA ROAD</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Former Director, 10% holder</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724585</rptOwnerCik>
            <rptOwnerName>EQC Private Markets SAC Fund II Ltd-EQC Biotech Sely S Fund</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724529</rptOwnerCik>
            <rptOwnerName>EQC Private Markets SAC Fund Ltd-EQC Biotech Sely I Fund</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724530</rptOwnerCik>
            <rptOwnerName>EQC Private Markets SAC Fund Ltd-EQC Biotech Sely II Fund`</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BERMUDIANA ROAD</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724701</rptOwnerCik>
            <rptOwnerName>Equilibria Capital Management Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BERMUDIANA ROAD</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724523</rptOwnerCik>
            <rptOwnerName>Castilian Ltd.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BERMUDIANA ROAD</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724811</rptOwnerCik>
            <rptOwnerName>Varibobi Financial Holdings Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIABRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>O'HARA HOUSE, ONE BERMUDIANA ROAD</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724558</rptOwnerCik>
            <rptOwnerName>Tafur Daniel</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BERMUDIANA ROAD</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState>D0</rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription>BERMUDA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001724539</rptOwnerCik>
            <rptOwnerName>EQC Private Markets II SAC Fund Ltd-EQC Biotech Sely III Fund</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EQUILIBRIA CAPITAL MANAGEMENT LTD.</rptOwnerStreet1>
            <rptOwnerStreet2>ONE BERMUDIANA ROAD</rptOwnerStreet2>
            <rptOwnerCity>HAMILTON</rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode>HM08</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-09-24</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1521863</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-09-24</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>676324</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-09-24</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F5"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>325799</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">EQC Private Markets SAC Fund II Ltd-EQC Biotech Sely S Fund (&quot;Sely S&quot;) distributed 1,521,863 shares to its partners on a pro rata basis, for no consideration.</footnote>
        <footnote id="F2">As a partner of Sely S, Fabio Lopez, received 19,524 of the shares distributed by Sely S.</footnote>
        <footnote id="F3">EQC Private Markets SAC Fund Ltd-EQC Biotech Sely I Fund (&quot;Sely I&quot;) distributed 676,324 shares to its partners on a pro rata basis, for no consideration.</footnote>
        <footnote id="F4">As partners of Sely I, Daniel Tafur and Equilibria Capital Management received 13,871 and 107,619, respectively, of the shares distributed by Sely I.</footnote>
        <footnote id="F5">EQC Private Markets SAC Fund Ltd-EQC Biotech Sely II Fund (&quot;Sely II&quot;) distributed 325,799 shares to its partners on a pro rata basis, for no consideration.</footnote>
        <footnote id="F6">As partners of Sely II, Fabio Lopez and Daniel Tafur received 6,325 and 2,372, respectively, of the shares distributed by Sely II.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Fabio Lopez, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>EQC Private Markets SAC Fund II Ltd EQC Biotech Sely S Fund, Daniel Tafur, Director, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>EQC Private Markets SAC Fund Ltd EQC Biotech Sely I Fund, Daniel Tafur, Director, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>EQC Private Markets SAC Fund Ltd EQC Biotech Sely II Fund, Daniel Tafur, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>EQC Private Markets II SAC Fund Ltd EQC Biotech Sely III Fund, Daniel Tafur, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Equilibria Capital Management Limited, Daniel Tafur, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Castilian, Ltd., Daniel Tafur, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Varibobi Financial Holdings Ltd., Fabio Lopez, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Daniel Tafur, by /s/ Ron A. Metzger, Attorney-in-Fact</signatureName>
        <signatureDate>2018-09-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
