The Third Dáil was the incarnation of Dáil Éireann that existed from 9th September, 1922 until 9th August 1923. The Third Dail was also known as the "Constituent Assembly" and the "Provisional Parliament". After 6th December, 1922 it served as the lower house of the Oireachtas (parliament) of the newly established Irish Free State.
The Third Dáil was elected under the terms of the Irish Free State (Agreement) Act, 1922 which was, in turn, enacted to give effect to the provisions of the 1921 Anglo-Irish Treaty and pave the way for the establishment of the Irish Free State. The Constitution of the Irish Free State provided, within its own articles, that it would not come into effect until it had been adopted by both the British Parliament and the Third Dáil, which it referred to as the "constituent assembly".
The elections to the Third Dáil took place on 16th June, 1922. They occured under the system of proportional representation by means of the Single Transferable Vote. Unlike the Second Dáil, which was notionally elected by the whole island of Ireland, the Third Dáil would not include members elected in Northern Ireland. Since the election of the Second Dáil in 1921, Sinn Fein, the only political party represented in the Dáil, had split into pro and anti-treaty factions and these two factions became the major contestants of the 1922 elections. The elections were therefore effectively a referendum on the Anglo-Irish Treaty. In the event the pro-treaty side won a majority of seats and the anti-treaty faction boycotted the assembly, refusing to recognise the body as the legitimate heir to the Second Dáil. The Civil War broke out shortly afterwards.
The Third Dáil adopted the Constitution of the Irish Free State on 25th October, 1922. The document was then enacted by the British Parliament and came into force on the 6th December. The new constitution used the name Dáil Éireann for the lower house of a new parliament called the "Oireachtas". However it provided that until the first elections to this new lower house the "constituent assembly" would exercise "all the powers and authorities" conferred on the 'new' Dáil Eireann. The Third Dáil therefore functioned as a legislative lower house from December, 1922 until it was dissolved on 9th August, 1923.
The Fourth Dáil, the first Dáil Éireann of the Irish Free State, was convened one month later in September. In spite of the nomenclature preferred by nationalists, under British constitutional theory it was this first Free State Dáil that was the first legitimate Irish political institution to bear the name "Dáil Éireann".