Interrupting his teaching, he pursued a Doctorate of Theology at the Catholic University of Louvain in Belgium, and received his degree in 1976.
Bustros then served for eleven years as director of the St. Paul Institute of Philosophy and Theology at the Paulist Missionaries at Harissa.
In 1988 the Holy Synod of the Melkite Catholic Church elected him Archbishop of Baalbeck, succeeding Elias Zoghby.
He was consecrated to the episcopate on November 27, 1988, in the Basilica of St. Paul in Harissa by Maximos V Hakim, assisted by Archbishops Zoghby and Joseph Raya.
Bustros was appointed to lead the Eparchy of Newton in the United States on June 22, 2004, succeeding John Elya.