The Lord Bishop of Leighlin was a separate episcopal title which took its name after the small town of Old Leighlin in County Carlow, Ireland.
In the Church of Ireland, it is held by the Lord Bishop of Cashel and Ossory, whose full title is the Lord Bishop of Cashel, Waterford, Lismore, Ossory, Ferns and Leighlin.
In the Catholic Church, it is held by the Lord Bishop of Kildare and Leighlin.
In the Church of Ireland, Leighlin was combined with Ferns in 1597 to form the united bishopric of Ferns and Leighlin.
The formal union of Kildare and Leighlin was decreed on 29 November 1694, thereby forming the united Diocese of Kildare and Leighlin.