Gregory (Gréne) (d. 1161), fifth bishop and first archbishop of Dublin, was chosen as successor to Bishop Samuel Ua hAingliu (qv) by a section of the people and clergy of Dublin. It seems that he was only a young sub-deacon when chosen; he was sent to England, where he was consecrated (2 October 1121) by Archbishop Ralph d'Escurs at Lambeth. While he was in England, Cellach (qv), archbishop and abbot of Armagh, entered his diocese, leaving Malachy (qv) to govern the church of Armagh in his absence. The Annals of Ulster describe the episode thus: ‘Cellach took the bishopric of Áth Cliath by choice of the foreigners and of the Gaedhil.’ His intention was apparently to force the diocese of Dublin to accept the episcopal jurisdiction of Armagh.
When Gregory returned to his diocese after his consecration he was refused entry, whereupon he returned to Archbishop Ralph at Canterbury, with whom he remained till the latter's death in the autumn of 1122. Eventually (c.1122), with the active intervention of Tairdelbach Ua Conchobair (qv), king of Connacht, Armagh's claims were overruled and Gregory re-entered his diocese, which he occupied till his death. It is likely, however, that Armagh retained some control over the diocese till the death of Cellach.
During Gregory's episcopate a Cistercian community from Savigny in Normandy founded a house at St Mary's, just outside the walls of Dublin. At the synod of Kells–Mellifont (1152), at which Ireland was finally divided into four archdioceses under Armagh, Tuam, Cashel, and Dublin, Gregory received the pallium of the archdiocese of Dublin from Iohannes Cardinal Paparo (qv). Five suffragan dioceses were assigned to Dublin: Glendalough, Ferns, Kildare, Leighlin, and Kilkenny. Gregory was later present at the solemn consecration of the abbey church of Mellifont along with the archbishops of Armagh and Tuam and the papal legate and bishop of Lismore, Christian Ua Conairche (qv). Following Gregory's death (October 1161), Lorcán Ua Tuathail (qv) was raised to the metropolitan see by Diarmait Mac Murchada (qv), king of Leinster.