Stack was arrested and sentenced to death for his involvement in the Rising, however, this was later commuted to penal servitude for life. He was released under general amnesty in June 1917 and was elected as an abstentionist Sinn Féin MP for Kerry West in the 1918 Westminster election, becoming a member of the 1st Dáil. He was automatically elected as an abstentionist member of the House of Commons of Southern Ireland and a member of the 2nd Dáil as a Sinn Féin TD for Kerry–Limerick West at the 1921 elections.