Thuc had entered the junior seminary in Anninh at the age of 12. He spent eight years there before going on to study philosophy at the major seminary in Hué. After his ordination to the priesthood on December 20, 1925, he taught at the Sorbonne in Paris. He was then selected to study theology in Rome and returned to Vietnam in 1927 after being awarded three doctorates from the Pontifical Gregorian University in Rome in philosophy, theology, and canon law.
In 1938, at the age of 41, Father Thuc was chosen by Rome to direct the Apostolic Vicariate at Vinhlong. He was consecrated bishop on May 4, 1938, being the third Vietnamese priest raised to the rank of bishop. On November 24, 1960, Pope John XXIII named Bishop Thuc Archbishop of Hué.
Thuc's brother, Ngo Dinh Khoi was buried alive because of his refusal to become a minister in the first communist government. Thuc's three other brothers, Ngo Dinh Diem, president of South Vietnam, Ngo Dinh Nhu and Ngo Dinh Can, his close collaborators were all assassinated. President Diem was assassinated on November 1, 1963. Of all his siblings, only Thuc and Luyen escaped assassination. Luyen was serving as ambassador in London and Thuc had been summoned to Rome for the Second Vatican Council. After the Council, for political reasons, Archbishop Thuc was not allowed to return to his duties at home thus beginning his life in exile.
Palmar de Troya, Spain, a town just outside of Seville, was the site of supposed apparitions of the Virgin Mary in the late 1960s and the 1970s. The visionary and founder of the Palmarian sect, Clemente Domínguez y Gómez staged ecstasies and received the stigmata. Due to the intervention of Archbishop Marcel Lefebvre, who ran a traditional Catholic seminary in Ecône, Switzerland, Archbishop Thuc began work with Palmar de Troya group. On January 11, 1976 Archbishop Thuc consecrated Dominguez Gomez and four others bishop after having first ordained them priest earlier. Since these actions were not done with the Vatican's approval, Pope Paul VI excommunicated Archbishop Thuc. Archbishop Thuc promptly broke with Palmar de Troya and Dominguez Gomez and his followers proceeded to perform mass, priestly ordinations and Episcopal consecrations effectively setting up a parallel church in schism with Rome. Upon the death of Pope Paul VI, Dominguez Gomez claimed to have been mystically crowned pope in a jail only hours after the death news reached him.May 7, 1981 he consecrated a Dominican priest, Guérard des Lauriers. On October 17, 1981, he consecrated two Mexican priests, Moises Carmona of Acapulco and Adolfo Zamora. On September 25, 1982, he consecrated Christian Marie Datessen. It is also alleged that during this period, Archbishop Thuc consecrated various individuals of dubious character.
It is alleged (by the Vezelis group in particular) that Archbishop Thuc was abducted by a group of Vietnamese priests while in New York and was taken to Missouri and hidden away from the contact of his friends. There he was subsequently held incommunicado.