A normalien and agrégé in mathematics, Michel-Louis Guérard des Lauriers entered the Dominican novitiate of Amiens in 1927 and was ordained a priest on 29 July 1931. He was an Invited Speaker of the ICM in 1932 in Zurich. He became a professor of philosophy at the Dominican school of theology, Le Saulchoir, in Belgium in 1933. In 1940, he received a doctorate in mathematics with thesis Sur les systèmes différentiels du second ordre qui admettent un groupe continu fini de transformations. Under Pope Pius XII, Fr. Guérard des Lauriers served as a professor at the Pontifical Lateran University in Rome. Some time prior to 1950, Guérard des Lauriers, O.P., was an advisor to the Pope on the dogma of the Assumption of Mary. From 1954 until 1955 he served as personal Father Confessor to Pius XII, before being replaced by Fr. Augustin Bea, S.J. With the advent of the Second Vatican Council in the 1960s, Guérard des Lauriers became concerned with events taking place in the Church. In 1969 he co-authored the Ottaviani Intervention which was a critical study of the new Mass. In 1970 Pope Paul VI made public a document demanding the resignation of certain conservative professors at the pontifical universities of Rome, among them Guérard des Lauriers. In 1979, worried about Archbishop Lefebvre and a possible deal with Rome among other things, Fr. Lauriers wrote to Lefebvre warning him.
Guérard des Lauriers then became a lecturer and professor at Archbishop Marcel Lefebvre's St. Pius X seminary in Écône, Switzerland. He then presented his thesis that the Chair of Peter might be vacant because Pope Paul VI was guilty of heresy. Because of this view, Lefebvre removed Guérard des Lauriers from his seminary teaching post in 1977. He further developed his beliefs on the current state of the papacy, relying on Cardinal Cajetan and St. Robert Bellarmine, arguing that Pope Paul VI, as a result of his heresy, was not a true pope, being only pope materially and not formally, known as the "Cassiciacum thesis". Guérard des Lauriers further believed that the new rites of ordination and episcopal consecration promulgated by Pope Paul VI were doubtfully valid and therefore it was necessary to take action to secure a valid succession of bishops for the preservation of the Roman Catholic Church. He began discussions with Dr. Eberhard Heller and Dr. Hiller, German sedevacantist activists who were harboring Most. Rev. Pierre Martin Ngô Đình Thục, the former archbishop of Huế, Vietnam, and after des Lauriers agreed to abate his Sedeprivationism and adhere to the theoretical tenets of Sedevacantism, it was agreed that the Archbishop Emeritus would consecrate him as a bishop. After long consideration, on 7 May 1981, des Lauriers was consecrated bishop by Ngo Dinh Thuc in Toulon, France. Shortly after, des Lauriers reiterated his Sedeprivationism and commenced a polemical war with the Sedevacantists, including Ngô Đình Thuc and Drs. Heller and Hiller. Guérard des Lauriers died in Cosne-sur-Loire, France, in 1988 at the age of 90.
Writings
By Guérard des Lauriers
Le Saint-Esprit, âme de l'Eglise, Étiolles, Seine et Oise : Monastère de la Croix, 1948.
Garabandal, S.l., 1965.
Lettera ad un religioso di Simone Weil ; trad. di Mariella Bettarini. Risposta alla Lettera ad un religioso di Guérard des Lauriers ; trad. di Carmen Montesano, Torino : Borla, 1970.
La Mathématique, les mathématiques, la mathématique moderne, Paris : Doin, 1972.
