Government of Ireland Act 1920 (Parliamentary and Dáil constituencies)

The Government of Ireland Act 1920 (10 & 11 Geo. 5 c. 67) was an Act passed by the Parliament of the United Kingdom which provided for parliamentary constituencies in the House of Commons of Northern Ireland and the House of Commons of Southern Ireland. Sinn Féin used these constituencies to elect the Second Dáil (1921–22) and the Southern Ireland ones to elect the Third Dáil (1922–23).

Sinn Féin decided to use these constituencies (in both parts of Ireland), for the purposes of the revolutionary Dáil Éireann. The 1921 elections were used to elect the Second Dáil. These seats replaced the Parliament of the United Kingdom constituencies provided for by the Redistribution of Seats (Ireland) Act 1918 (7 & 8Geo. 5 c. 65). These had been used as Dáil constituencies for the First Dáil.

The number of seats was increased from 105 to 180 (52 in Northern Ireland and 128 in Southern Ireland, subsequently the Irish Free State).