The auxiliary bishop of Armagh has retired because of ill health.
Gerard Clifford worked closely with Cardinal Sean Brady but has been receiving medical advice since August.
He was auxiliary bishop in Armagh for 21 years but his resignation has been accepted by Pope Benedict.
"It is with great sadness that I come to today's decision," he said.
Bishop Clifford was born near Dundalk, Co Louth, and ordained as a priest in 1967. The former executive secretary of the Irish Catholic Bishops' Conference has worked on ecumenism, education and pastoral care in cases of "crisis pregnancy". He has been president of the church's pro-life crisis pregnancy counselling service Cura since 2010.
The clergyman has also undertaken work with the Church of Ireland aimed at establishing closer relations.
"Having grown up locally in the diocese - born in the parish of Lordship & Ballymascanlon in 1941 - and as priest and auxiliary bishop in the Archdiocese of Armagh, I have received great warmth and affection throughout my ministry from the people of the diocese," he said.
"I thank them for their support in my 21 years as auxiliary bishop."
He said Cardinal Brady had been a model episcopal colleague. "His humanity, deep faith and natural humility bear witness to the most fundamental of Gospel values," he said.
Cardinal Brady is expected to be succeeded as Archbishop of Armagh by Monsignor Eamon Martin, the administrator of the Diocese of Derry, who was appointed co-adjudicator earlier this year.