Some Swiss laymen offered the International Seminary of Saint Pius X at Écône to the newly formed group, and in 1971 the first 24 candidates entered, followed by a further 32 in October 1972.

(Since 1983, the term ' association of the faithful' has replaced 'pia unio'.) The Society of Saint Pius X was formally founded, adhering to all canonical norms, and receiving the episcopal blessing and encouragement of the local ordinary. Pia unio status was the first stage through which a Catholic organisation passed prior to gaining official recognition as a religious institute or society of apostolic life. Pius X as a pia unio (Latin, for 'pious, or holy, union') on a provisional ( ad experimentum) basis for six years. Charrière granted Lefebvre's request and, with a document predated by six days to 1 November 1970, he established the Society of St. He told them, if he said to go through with it, he would see in it a sign of Divine Providence. In late 1970, at age 65, urged by the abbot of Hauterive Abbey and the Dominican theologian Father Marie-Dominique Philippe to teach the seminarians personally, Lefebvre, feeling too old to undertake such a large project, told them he would visit François Charrière, Bishop of Lausanne, Geneva and Fribourg, with a request to set up a religious society. He directed them to the University of Fribourg, in Switzerland. They sought Lefebvre's advice on a conservative seminary where they could complete their studies. In September 1970, shortly after his retirement as Superior General of the Congregation of the Holy Spirit, Lefebvre was approached by eleven members of the Pontifical French Seminary in Rome. The founder and central figure of the society was the French Archbishop Marcel Lefebvre, who had served the Catholic Church as Apostolic Delegate for French-speaking Africa, Archbishop of Dakar, and Superior General of the Congregation of the Holy Spirit, a missionary order of priests. Like Traditionalist Catholicism in general, the SSPX was born out of opposition to changes in the Catholic Church that followed the Second Vatican Council (1962–1965). Lefebvre, the society's founder, celebrating Tridentine Mass While its critics claim the society's priests were not explicitly granted the requisite jurisdiction, it contends that they possessed 'supplied jurisdiction' for confessions due to a ' state of necessity'. The significance of these recognitions is that, unlike other Catholic sacraments, both confession and marriage require canonical jurisdiction for their validity. In addition, the Holy See named SSPX bishop Fellay as judge in a canonical trial against one of the society's priests. The 2010s saw growing recognition by the Holy See of its sacramental and pastoral activities, with Papal recognition extended indefinitely in 2017 to confessions heard by its priests, and local ordinaries allowed to grant delegation to its priests for officially witnessing marriages. The society's canonical situation remains unresolved. Though the SSPX denied that the bishops incurred any penalty, claiming canon law in their defense, the declared excommunication of the surviving bishops was at their request removed in 2009 in the hope of speedily reaching 'full reconciliation and complete communion'. Tensions between the society and the Holy See reached their height in 1988 with the Écône consecrations: Archbishop Lefebvre consecrated four bishops without the Apostolic Mandate and against a personal warning by Pope John Paul II, resulting in Rome declaring that the bishops who consecrated or were consecrated had incurred latae sententiae (automatic) excommunication. There are a number of organisations derived from the SSPX: most notably the Society of Saint Pius V (SSPV), a group mostly in the United States and the Priestly Fraternity of Saint Peter (FSSP), which was made a society of apostolic life under Pope John Paul II in 1988. The present Superior General of the society is the Reverend Davide Pagliarani, who succeeded Bishop Bernard Fellay in 2018.

The society is named after Pope Pius X, whose anti- Modernist stance the society stresses, retaining the Tridentine Mass and pre-Vatican II liturgical books in Latin for the other sacraments. In 2022, the society reached over 700 priestly members, with 1,135 total members.

The society was initially established as a pious union of the Catholic Church with the permission of François Charrière, the Bishop of Lausanne, Geneva and Fribourg in Switzerland. The Society of Saint Pius X ( SSPX) ( Latin: Fraternitas Sacerdotalis Sancti Pii X FSSPX) is an international fraternity of traditionalist Catholic priests founded in 1970 by Archbishop Marcel Lefebvre, a leading traditionalist voice at the Second Vatican Council with the Coetus Internationalis Patrum, and Superior General of the Holy Ghost Fathers until 1968.

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