Irish statesman and first president (1922–32) of the Irish Free State.

At an early age, Cosgrave was attracted to the Irish nationalist movement Sinn Féin. He became a member of the Dublin Corporation in 1909 and was subsequently reelected in the Sinn Féin interest. When Britain entered World War I, he joined the Irish Volunteers; but when this group split in 1914, Cosgrave sided with a radical Sinn Féin minority against the moderates led by John Redmond.

Cosgrave took part in the Easter Rising (1916) and was afterward interned by the British for a short time. In 1917 he was elected to Parliament for the city of Kilkenny. In the sweeping election victory of the Sinn Féin in 1918, he became a member of the first Dáil Éireann, the Irish Assembly. He was made minister for local government in the first republican ministry; and, during the struggle with the British, his task was to organize the refusal of local bodies to cooperate with the British in Dublin.

Cosgrave was a supporter of the 1921 treaty settlement with Great Britain, and he became minister of local government in Ireland's newly formed provisional government. Cosgrave replaced Michael Collins as chairman of the provisional government when the latter became commander-in-chief of the army in July 1922. Cosgrave also replaced Arthur Griffith as president of the Dáil after Griffith's sudden death on August 12. As the first president (from December 1922) of the executive council of the Irish Free State, Cosgrave represented Ireland at the Imperial Conference in October 1923; and a month earlier he was welcomed as Ireland's first spokesman at the assembly of the League of Nations.

Cosgrave restored settled government in Ireland. In the Dáil there was no serious opposition, since the party headed by Eamon De Valera, which refused to take the oath prescribed in the treaty, abstained from attendance. But neither Cosgrave nor his ministry enjoyed much popularity. Order required drastic measures, and taxation was heavy and sharply collected. Cosgrave seemed sure of a long tenure only because there was no alternative in sight. In July 1927, shortly after the general election, the assassination of Kevin O'Higgins, the vice president, produced a crisis. Very severe legislation against political associations of an unconstitutional character was introduced, and a bill declaring that no candidature for the Dáil should be accepted unless the candidate declared himself willing to sit and to take the oath of allegiance. The result of this measure was that De Valera and his party decided to attend sessions in the Dáil, and, since this greatly altered the parliamentary situation, Cosgrave obtained leave to dissolve the assembly and hold a general election. The election in September 1927 left his party numerically the largest in the Dáil but without an overall majority. He continued in office until De Valera's decisive victory at the general election of 1932. In 1944 Cosgrave resigned from the leadership of the United Ireland Party (Fine Gael).