At the 1918 general election, he was Sinn Féin's Director of Finance and the party's fourth Director of Elections (his three predecessors having been imprisoned). He was elected as a Sinn Féin MP for his old constituency of Kilkenny South, defeating the Irish Party's Matthew Keating by 8,685 votes to 1,855. South Kilkenny was one of 73 constituencies returning Sinn Féin MPs pledged not to take their seats at Westminster. In the First Dáil Éireann he became Trustee of Dáil Éireann funds, and travelled to the United States with Éamon de Valera to pursue a fund-raising drive. He resigned his trusteeship and his Dáil seat in 1921 after a disagreement with de Valera.