On petition of King Edward II, Pope John XXII issued a papal bull for the union of the Dioceses of Cork and Cloyne on 30 July 1326, with effect from the death of either bishop.

The union should have taken effect on the death of Philip of Slane in 1327, but bishops were still appointed to both dioceses.

The dioceses were eventually united on the episcopal appointment of Jordan Purcell on 15 June 1429, following their impoverishment from the robbery of church property by the nobility.

[1] From 1693 to 1747, the Bishop of Cork and Cloyne was also the apostolic administrator of the Diocese of Ross.

The diocesan boundary with the neighbouring Diocese of Cloyne roughly follows the course of the River Lee.