The Diocese of Dromore was established through the reorganisation of the Irish Church in the late 12th century, possibly at the synod held in Dublin in 1192[1] by the papal legate, Múirges Ua hÉnna, Archbishop of Cashel.

The diocese coincided with the territory of the Uí Echach Cobo, which later became the baronies of Upper and Lower Iveagh, and the lordship of Newry, County Down.

Work for building of Newry Cathedral begun in 1823 and was completed in 1829 [5] by Dr. Michael Blake (bishop of Dromore 1833–1860) who had been Vicar-General of Dublin and the restorer of the Irish College at Rome.

It is called in the annals Monasterium de Viridi Ligno — a name given to Newry from the yew-tree, said to have been planted there by St. Patrick, the Irish name being Niubar (and sometimes Newrkintragh, "the yew at the head of the strand") which is Latinized Ivorium or Nevoracum, but more commonly as above Viride Lignum.

In 2012 the parish priest of Donaghmore in the diocese, Terence Rafferty, was convicted of four counts of indecently assaulting a young girl in 2001.

Pope Francis accepted McAreavey's resignation on 26 March 2018 and Bishop Philip Boyce was appointed Apostolic Administrator.

[8] On 15 April 2019, Pope Francis appointed the Archbishop of Armagh Eamon Martin as Apostolic Administrator of the diocese.