He lectured in the Mater Dei Institute of Education from 1969, becoming professor of moral theology at Clonliffe College.[1] He also lectured at UCD – from 1973 to 1982 in Catechetics and from 1978 to 1982 in Medical Ethics.[1]
In 1981 he was appointed Titular Bishop of Glenndálocha and Auxiliary Bishop of Dublin, making him the youngest bishop at the time, aged only 41.[1] He was appointed as bishop of Limerick on 10 February 1996 by Pope John Paul II. He was installed as Bishop of Limerick on 24 March 1996.[1]
In November 2009, he was pressured to resign from his post after the Murphy Report found that he had mishandled child sexual abuse allegations within his diocese.[2]
He announced his resignation to a congregation, including priests of the Diocese, people working in the Diocesan Office and the Diocesan Pastoral Centre, at 11 am (noon in Rome, the hour of the publication of the decision) in St. John's Cathedral, Limerick.[3]