The Diocese of Ardagh and Clonmacnoise (Latin: Dioecesis Ardachadensis et Cluanensis; Irish: Deoise Ardach agus Chluain Mhic Nóis) is a Latin Church diocese of the Catholic Church in Ireland.

The main towns in the diocese are Athlone, Ballymahon, Carrick-on-Shannon, Edgeworthstown, Granard and Longford.

[1][2] On Christmas Day 2009, St Mel's cathedral in Longford was destroyed by fire.

After a long investigation the cause of the fire was traced back to a brick lined chimney at the rear of the cathedral.

On 5 April 2023, Paul Connell was appointed the Bishop of Ardagh and Clonmacnoise by Pope Francis.