 After six years of further studies in Rome, he was appointed in 1959–1967 as a faculty member and rector of the Seminary of Hoan Thiện, Huế.He was appointed Bishop of Nha Trang on 13 April 1967 and received episcopal consecration on 4 June 1967 at Huế from Angelo Palmas, Apostolic Delegate to Viêt Nam (and later Nuncio to Colombia and to Canada), assisted by Bishops Philippe Nguyễn Kim Dien, Apostolic Administrator, "sede plena", of Huế, and Jean-Baptiste Urrutia, titular archbishop of Carpato.On 24 April 1975, he was appointed Coadjutor Archbishop of Saigon.