Bishop Willie Walsh has reached retirement age.
Fr Kieran O'Reilly has been appointed to succeed Bishop Willie Walsh as the new Bishop of Killaloe, which covers mainly County Clare.
Bishop Walsh is leaving his post after reaching the bishop's retirement age of 75.
He was not one of the bishops criticised in the Murphy report into an abuse cover in the Irish church.
His successor, Fr O'Reilly, is a member of the missionary order the Society of African Missions.
In 2001 he was elected Superior General of the society and was re-elected for a second term of office in 2007. He is currently based in Rome.