The Chapel Royal in Dublin Castle was the official Anglican chapel of the Household of the Lord Lieutenant of Ireland from mediæval times until the creation of the Irish Free State in 1922. The creation of the new Irish state terminated the office of Lord Lieutenant and his British government regime in Ireland, which had been based in Dublin Castle.

The coat of arms of each Lord Lieutanant was placed at some location within the Chapel. It was noted by Irish nationalists that the last available space for arms was taken up by the man who proved to be the last Lord Lieutenant, Viscount Fitzalan

In 1943, the former Anglican church became a Roman Catholic Church, under the name the Church of the Most Holy Trinity. Though it has not been deconsecrated, neither Masses nor Divine Services take place there any more. It has however been recently restored to its eighteenth century state, with its victorian decoration removed.