On his return to Ireland, Clarke acted as the courier for the First Dáil[4] and served as an usher at the first meeting of the First Dáil.[5] He was interned from January 1921.[6] Released in 1923, he acted as caretaker of the Sinn Féin headquarters on Harcourt Street,[4] and founded the Irish Book Bureau.[3] Although the Anti-Treaty Sinn Féin rejected participation in the Dáil, they continued to contest local elections, and Clarke sat on Dublin City Council.[7]
Although Clarke had served under Éamon de Valera during the Easter Rising, the two became implacable opponents. Clarke was ejected from an official commemoration of the fiftieth anniversary of the First Dáil for interrupting de Valera's speech in order to raise the complaints of the Dublin Housing Action Committee.[12] He vowed to outlive de Valera, he succeeded in this endeavour by outliving him a year.[13]
Clarke was elected as a Vice-President of Sinn Féin in 1966. In the split of 1970, he supported the provisional wing, remaining Vice-President.[14] The Dublin South West Inner City cumann of Sinn Féin is named for Clarke.[3]
