The diocese of Mayo was not established at the
Synod of Rathbreasail in 1111, but was recognised at the
Synod of Kells in 1152. A bishop of Mayo, probably Gille Ísa Ua Maílín, took the oath of fealty to
King Henry II of England in 1172. The bishopric in some way represented the lordship of
Muirchertach Muimhnech Ua Conchobair taniste of Connacht, who died in 1210, and his family
Clan Murtagh O'Conor, who controlled the area up to the 1230s. In 1202, the papal legate, Cardinal John, had the
see of Mayo united to the
archbishopric of Tuam. In 1216,
Pope Innocent III heard the case in Rome, and gave sentence in favour of Tuam. His sentence was maintained by papal legate James in 1221, and was finally confirmed by
Pope Gregory IX on 3 July 1240. However, in the first half of the fifteenth century, Mayo appears to have gained independence with further bishops of Mayo being appointed, although their position is unclear and may have been assistant or suffragan bishops. Following the
Reformation, there were parallel successions in the Church of Ireland and the
Roman Catholic Church. Circa 1559, the see was united with the
archbishopric of Tuam in the
Church of Ireland. The Roman Catholic see continued until the early seventeenth century, when, after a long vacancy, it was united into the
archdiocese of Tuam in 1631. ==List of bishops==