The 62-year-old, appointed four years ago as Bishop of Killaloe, will succeed Archbishop Dermot Clifford, who has retired.
He currently serves as secretary to the Irish Episcopal Conference. Born in Turner’s Cross in Cork City, he was educated at Scoil Chríost Rí and Coláiste Chríost Rí before joining the Society of African Missions in 1970.
The Primate of All Ireland, Archbishop Eamon Martin, congratulated Bishop O’Reilly on behalf of the Irish Episcopal Conference.
“I have known Archbishop Kieran since he became Bishop of Killaloe in 2010,” he said. “In that time, like the people of Killaloe, I have come to know the warmth of his personality and his gentleness and pastoral sensitivity.
“As a new bishop myself, I have appreciated his wise counsel on many matters.”
Archbishop Clifford had been Ireland’s longest serving archbishop.
He was appointed Coadjutor Archbishop of Cashel & Emly in 1986 to the late Dr Thomas Morris, and later Archbishop in 1988.
Archbishop Clifford said: “I always prayed that I would be here and well enough to ordain my successor when I reached retirement age.
“As it turns out, I now find that I have already ordained him four years ago in Ennis — that he is a scholar I learned from others, that he is a gentleman I have found out for myself.”
Bishop O’Reilly served in Liberia for two years after being ordained in 1978. In the mid- to late-1980s, he lectured in Scripture at the seminary of Sts Peter and Paul in Ibadan, Nigeria.
From 1989 until his appointment as Bishop of Killaloe in 2010, he served on the Irish and International Councils of the Society of African Missions.
Archbishop Martin, meanwhile, said Bishop O’Reilly “brings a perspective to the table of the Irish Episcopal Conference which is drawn from his wide experience of mission in Liberia and Nigeria. Conscious of Pope Francis’ dream, mentioned in his Apostolic Exhortation (The Joy of the Gospel), of a ‘missionary option’ to inspire everything we do in the Church, I have no doubt that Archbishop Kieran will continue to make an invaluable contribution to the renewal and mission of the Church in Ireland.”
Archbishop Martin also recalled how, in more recent times, Archbishop Clifford had acted as Apostolic Administrator in the Diocese of Cloyne following the resignation there of Bishop John Magee due to mishandling of clerical child sex abuse allegations in that diocese.
“For this, the Church in Ireland, and indeed the Universal Church, owe him a great debt of gratitude for his tireless and selfless service during the most challenging of times,” Archbishop Martin said.
Bishop O’Reilly will become one of four Catholic Archbishops in Ireland when he is installed at the Cathedral of the Assumption in Thurles on February 8, and joins Archbishop of Armagh Eamon Martin, Archbishop of Dublin Diarmuid Martin, and Archbishop of Tuam Michael Neary.