For decades, he not only lived in schism. With unauthorised episcopal ordinations, he laid the foundations for the ordination lines of many vagrant priests and bishops who are still active today and who are up to mischief almost everywhere in the world.
Vagrants are clergy who are not subject to any proper Catholic hierarchy. There is hardly a curious church scandal without clergymen who claim to be ordained in the line of ordination of Thục: From the bishop in charge of the schismatic Poor Clares in Belorado via the "Palmarian Catholic Church" all the way to the "Pegida bishop" Markus R. and Ralph N. with his movement "Maria 3.0"which German bishops have been warning against for years, the list goes on.
Thục was born in 1897 to a wealthy Catholic civil servant family while Vietnam was still an empire. At the age of twelve, he entered the boys' seminary in An Ninh, later studied at the seminary in Huế and was ordained a priest in 1925.
In Rome, he studied philosophy, theology and canon law; it is sometimes said that he also obtained a doctorate in these subjects at the Pontifical Gregorian University.
However, there is no evidence of this in the university archives. After teaching briefly at the Sorbonne in Paris, he returned to Vietnam in 1927 and soon made a career for himself there: in 1938, he became Vicar Apostolic of Vĩnh Long. He was also consecrated a bishop for this office - and was allegedly also given a special mandate by Pope Pius XI in view of the turmoil of the French colonial rule, which was coming to a bloody end: an authorisation for all necessary powers "for the purposes known to us", including the power to consecrate bishops without consulting the Pope if necessary.
Promoted as anti-communists by the USA
Thục was not the only one in his family to make a career: his younger brother Ngô Đình Diệm was the first president of the southern part of Vietnam, the Republic of Vietnam, from 1955 until his assassination in 1963.
The USA had long supported the politician, who abolished the monarchy but came to office himself through rigged elections, as an anti-communist alternative to North Vietnamese President Hồ Chí Min: Both Thục and Diệm were regarded as reliable anti-communists in the USA in the 1950s, and both established contacts with the influential Archbishop of New York, Cardinal Francis Spellman, who lobbied Pope Pius XII in favour of Thục. Thục was instrumental in preparing for Diệm's political rise.
In 1960, Pope John XXIII established the archdiocese of Huế and made Thục its first archbishop - following Spellman's intercession. The decline of the Ngô family's influence in Vietnam was heralded by Thục's 25th anniversary as bishop: the celebrations in 1963 were supported with government funds and Vatican flags were to be hoisted.
In the same year, Buddhists in Huế were banned from displaying Buddhist flags on Buddha's birthday - the different treatment of the religions led to protests against the government, and a Buddhist monk manifesto calling for equal rights for Buddhists and Catholics fuelled the mood.
The image of the Buddhist monk Thích Quảng Đức, who burnt himself to death in protest, went around the world. It was only when a bomb - allegedly planted by the Viet Cong guerrilla organisation - killed nine people that the protests ended for the time being.
The regime struck back at the resistance movement with bloodshed. In November 1963, Diệm was deposed and murdered. Apart from Thục, only one other of the six Ngô brothers survived this period: Ngô Đình Luyện was in London as ambassador, Thục was in Europe on the occasion of the Second Vatican Council, probably in Lourdes at the time of the coup.
Council father in exile
Thục took part in all sessions of the Council. When the Council ended in 1965, the governments of Vietnam and the USA as well as the Vatican agreed that Thục should not return to his home country - thus began Thục's exile in Rome.
In 1968, he resigned as Archbishop of Huế; according to his own account, under pressure from Pope Paul VI, but also already in dissent from the decisions of the Second Vatican Council.
With his exile, Thục began to drift away.
As a mere titular bishop - the institute of the bishop emeritus had not yet been established - he had no task befitting his rank, but worked first in Italy, then in France, as an assistant clergyman.
During this time, he made contact with other opponents of the Second Vatican Council: in France, he came into contact with the movement surrounding the alleged Marian apparitions in El Palmar de Troya, Spain, through the mediation of the canon law professor at the seminary of the Society of St Pius X.
It was there that Thục conferred his first illegal ordination: Clemente Domínguez y Gómez, to whom the Virgin Mary had allegedly appeared, and other of his followers were ordained priests on the night of 1 January 1976; ten days later, Thục ordained Domínguez and four other men as bishops.
The forbidden episcopal consecration is punishable by excommunication, which was also pronounced immediately after it became known by the then Prefect of the Congregation for the Doctrine of the Faith, Cardinal Franjo Šeper.
The decree established three consequences of irregular consecrations: both the consecrator and the consecrated had incurred the penalty of excommunication as a result of the illegal episcopal consecration. Illegally ordained priests are suspended and thus prevented from exercising priestly ministries.
The third stipulation concerned the recognition of ordinations: "Finally, as regards those who have been ordained in this unlawful manner, or who may be ordained by them in the future, the Church does not and will not recognise their ordination; she considers them, as regards all juridical effects, in the state that each of them had before, and subjects them to the penal sanctions mentioned above until they repent."
Illegal ordinations - but also invalid ones?
However, one word is conspicuously missing from this decree: "invalid". Although the prefect stated that the Church does not recognise the ordinations, he did not clearly state whether this actually means that they are invalid - i.e. that apostolic succession has been ineffectively conferred due to the lack of a valid sacrament of ordination.
For an episcopal ordination to be valid, hardly anything is required apart from a validly ordained bishop who administers the ordination - unlike the sacrament of marriage, the Church has not laid down in detail the exact form that must be observed in order to lead to a valid sacrament.
Essentially, an ordination conferred by an ordained bishop would only be invalid if his state of mind did not allow him to confer the ordination.
However, there seemed to be no evidence of this in Thục's case, although it was repeatedly suspected and implied that he was regarded as "non compos mentis", not in full possession of his mental faculties, and therefore unable to validly consecrate.
The first excommunication was soon lifted: Thục concluded that the Marian apparitions of Palmar de Troya were not genuine and that he had made a mistake with his consecrations; his excommunication was lifted in 1976.
However, the "Palmarian Catholic Church" continued to exist: in 1978, after the death of Pope Paul VI, Domínguez declared himself "Pope Gregory XVII" on the basis of a new vision - and thanks to his episcopal consecration, the movement was able to invoke the Apostolic Succession.
Thục's peace with the Church did not last long: in 1981, he consecrated the sedisvacantist priest Michel-Louis Guérard des Lauriers as bishop, a former Dominican and advisor to Pope Pius XII.
A few months later, Thục consecrated two Mexican priests, Mosè Carmona and Adolfo Zamora - like Guérard des Lauriers, both assumed that the papal chair was vacant. At the beginning of 1982, Thục then positioned himself as clearly sedisvacantist with a manifesto and declared that the only valid Mass was that of St Pius V. St Pius V. who reformed the Roman missal in 1570 after the Council of Trent.
Thục opposed "modernism", "false ecumenism", a "cult of man", the recognition of religious freedom and his unwillingness to condemn heresies and cast out heretics: "Therefore, as bishop of the Roman Catholic Church, I judge that the see of the Roman Catholic Church is vacant, and it behoves me as bishop to do whatever is necessary for the Roman Catholic Church to persevere in its mission for the salvation of souls."
De-radicalisation in the USA
The Congregation for the Doctrine of the Faith, now under its prefect Joseph Ratzinger, counted in a declaration published in 1983 Guérard des Lauriers, Carmona and Zamora, the Congregation for the Doctrine of the Faith, now under its prefect Joseph Ratzinger, listed three other priests who had since been ordained bishops by Carmona. Cardinal Ratzinger renewed the statement that Thục and those ordained by him were excommunicated and suspended the priests they had ordained.
Doubts were now raised about the validity of the ordinations: "Finally, with regard to the validity of the ordinations of those who have already received ordinations in this unlawful manner or are about to receive them, the Church neither recognises nor will recognise these ordinations, whatever their validity may be, and considers these persons to belong to the state they occupied before these events." Ratzinger thus made it explicit that the Church had so far refrained from passing judgement on validity.
Thục moved to the USA in 1983 at the invitation of a bishop who was above Carmona in his line of ordination.
In the USA, Thục increasingly turned to pastoral care for the Vietnamese community and also reunited with friends from his own time in Vietnam. The encounters led to a deradicalisation: Thục turned away from sedisvacantism.
On 11 July 1984, he reconciled with the church, his excommunication was lifted and on 13 December he died in Carthage, Missouri, at the age of 87.
His legacy lives on: Thục is said to have illegally consecrated at least 15 bishops during his lifetime - today, countless sedevacantist, traditionalist and other schismatic vagrant clerics refer to him - and not only these.
Probably the best-known person who has invoked Thục's line of ordination was ordained in 1999 by the Irishman Michael Cox, who received his episcopal ordination from the Palmarians: the singer Sinéad O'Connor was ordained a priest by him in Lourdes and temporarily took the name "Mother Bernadette Marie".