The Archdiocese of Armagh is a Latin ecclesiastical territory or archdiocese of the Catholic Church located in the northern part of Ireland. The ordinary is the Roman Catholic Archbishop of Armagh who is also the Metropolitan of the ecclesiastical province of Armagh and the Primate of All Ireland. The mother church is St Patrick's Cathedral. The claim of the archdiocese to pre-eminence in Ireland as the primatial see rests upon its traditional establishment by Saint Patrick circa 445. It was recognised as a metropolitan province in 1152 by the Synod of Kells.

St. Patrick's Cathedral in Armagh, Northern Ireland is the seat of the Catholic Archbishop of Armagh, Primate of All Ireland. 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 retained by the state church, the Church of Ireland at the time of the split of the Irish Church during the Reformation.