However, by 1936, systematic attempts to remove references to the monarch from Irish constitutional law meant that the only functions remaining to the Crown were: This status quo remained, with Ireland participating little in the British Commonwealth and Éamon de Valera remarking in 1945 that "we are a republic" in reply to the question if he planned to declare Ireland as a republic.

[2] Then somewhat unexpectedly in 1948, during a visit to Canada, Taoiseach John A. Costello announced that Ireland was to be declared a republic.

When the Act came into force on 18 April 1949, it effectively ended Ireland's status as a British dominion.

The UK Secretary of State for Home Affairs explained that:[5] [w]hen British Nationality Act was passed the United Kingdom did not know that a person who was born in Southern Ireland of a Southern Irish father and on 6th December, 1922, was domiciled in Northern Ireland was regarded as a citizen of Eire under Eire law.

[5] In this regard he noted:[5] The important date to bear in mind there is 6th December, 1922, for that was the date...the Irish Free State was constituted, and as constituted on 6th December, 1922, it consisted of the 32 counties with the six counties which now form Northern Ireland having the right to vote themselves out.

Therefore, the Eire law, by inserting the date 6th December, 1922, and attaching to that the domicile, meant that anybody domiciled inside the island of Ireland on 6th December, 1922, was a citizen of Eire.The amendment made to the British Nationality Act under the Ireland Act was intended to make it clear, in summary, that regardless of the position under Irish law, the affected persons domiciled in Northern Ireland on 6 December 1922 would not be deprived of a British citizenship status they would otherwise have enjoyed but for Irish law.