A veteran of the 1916 Easter Rising, the War of Independence and the Civil War, Lemass was first elected as a Sinn Féin TD for the Dublin South constituency in a by-election on 18 November 1924 and was returned at each election until the constituency was abolished in 1948 when he was re-elected for Dublin South-Central until his retirement in 1969. He was a founder-member of Fianna Fáil in 1926 and served as Minister for Industry and Commerce, Minister for Supplies and Tánaiste in successive Fianna Fáil governments.