 He was educated at Bellurgan National School, Bush Vocational School, St Mary's College, Dundalk, and Saint Patrick’s College, Armagh.He studied for the priesthood at St. Patrick’s College, Maynooth and undertook postgraduate studies both in Maynooth and in the Jesuit Lumen Vitae, Brussels.Clifford was ordained a priest on 18 June 1967 for the diocese and was appointed an auxiliary bishop of Armagh and Titular Bishop of Hieron on 25 March 1991.