In 1968 he was accepted as a student for the Archdiocese of Birmingham and was ordained priest on 20 July 1974 in the Metropolitan Cathedral of St Chad in Birmingham. From 1976 to 1985 he was a lecturer in moral theology at Oscott College. He became secretary at the Pontifical Council for Promoting Christian Unity in Rome 1985-1993. McDonald earned a Doctorate of Sacred Theology from the Pontifical University of Saint Thomas Aquinas, "Angelicum" in 1989 with a dissertation entitled "Communion and friendship : a framework for ecumenical dialogue in ethics".