Ireland becomes a Republic
Only in the spring of 1923 did the Parliament of Northern Ireland and the Oireachtas in Dublin start to function normally.
The Westminster Parliament now governed the United Kingdom of Great Britain and Northern Ireland.
The British monarch, King George V, continued to be head of state in the Irish Free State, but the External Relations Act, 1936, reduced his role. Section 3 of that Act recognised George VI as his successor “under the law of Saorstát Eireann” and authorised him to act on its behalf “for the purposes of the appointment of diplomatic and consular representatives and the conclusion of international agreements”.
In 1937 a new Irish constitution established an elected president. There was disagreement between Ireland and the UK as to whether this mean Ireland was a republic.
In 1948 John A. Costello, the Taoiseach (the Irish prime minister), announced that legislation would remove the residual role of the King in Irish law. The subsequent Republic of Ireland Act, 1948, “hereby declared that the description of the State shall be the Republic of Ireland”.
The UK Parliament then passed the Ireland Act 1949, which acknowledged that Ireland had “ceased to be part…of His Majesty's dominions” and therefore a member of the Commonwealth.
The 1949 Act also clarified the status of Northern Ireland within the United Kingdom, giving a statutory guarantee that it would remain part of the UK so long as its devolved parliament desired.
This provision caused controversy among Irish nationalists who viewed it as an obstacle to achieving a united Ireland.