Bishop Moriarty, 65, was educated at, among other places, St. Patrick´s College in Maynooth. He was ordained a priest for the Archdiocese of Dublin in 1961.
He is currently chairman of the National Committee of Diocesan Youth Directors, and will be a speaker at World Youth Day in Toronto. He is also chairman of the episcopal Commission for Pastoral Renewal.
He will replace Bishop Laurence Ryan, who submitted his resignation last July.
The Diocese of Kildare and Leighlin has a Catholic population of 183,000 in 56 parishes, and includes County Carlow and parts of counties Kildare, Laois, Offaly, Kilkenny, Wicklow and Wexford.