It was built in various phases between 1840 and 1904 to serve as the Roman Catholic Cathedral of the Archdiocese of Armagh, the original medieval Cathedral of St Patrick having been transferred to the Protestant Church of Ireland at the time of the Irish Reformation. The Cathedral stands on a hill as does its Anglican counterpart.
The building of a Catholic cathedral at Armagh was a task imbued with great historic and political symbolism. Armagh was the Primatial seat of Ireland and its ancient ecclesiastical capital. Following Catholic emancipation in 1829, the need to construct churches and cathedrals to serve this population became apparent. The lack of a Catholic presence in the Primatial City of Armagh in particular became a popular cause of discontent among the emerging Catholic episcopacy, clergy and congregation. Although a start was made in building the Cathedral in 1838 building stopped from time to time, and significant redesigns occurred, so that it was not until 1904 that it could be completed.
The decorative style of the cathedral was significantly changed in 1982, followed by major structural repairs in 2002. The beautiful interior in particular has been frequently remarked upon by visitors.