The First Dáil (Irish: An Chéad Dáil) was Dáil Éireann as it convened from 1919 to 1921. It was the first meeting of the unicameral parliament of the revolutionary Irish Republic. In the December 1918 election to the Parliament of the United Kingdom, the Irish republican party Sinn Féin won a landslide victory in Ireland. In line with their manifesto, its MPs refused to take their seats, and on 21 January 1919 they founded a separate parliament in Dublin called Dáil Éireann ("Assembly of Ireland"). They declared Irish independence, ratifying the Proclamation of the Irish Republic that had been issued in the 1916 Easter Rising, and adopted a provisional constitution.

Its first meeting happened on the same day as one of the first engagements of what became the Irish War of Independence. Although the Dáil had not authorised any armed action, it became a "symbol of popular resistance and a source of legitimacy for fighting men in the guerrilla war that developed".

The Dáil was outlawed by the British government in September 1919, and thereafter it met in secret. The First Dáil met 21 times and its main business was establishing the Irish Republic. It created the beginnings of an independent Irish government and state apparatus. Following the May 1921 elections, the First Dáil was succeeded by the Second Dáil of 1921–1922.