At the beginning of 1782 he went to Vienna with Fr N. A. von Diessbach (q.v.), of whom he was the favourite pupil and active collaborator, to prepare for the arrival of Pius VI; in the same year, on 25 May, he was ordained priest and on 13 July obtained the degree in theology at the University of Turin. He consistently refused any office or benefice in order to devote himself solely to the apostolate, which he exercised in the confessional (he was a sought-after spiritual director), in the preaching of the Spiritual Exercises according to the Ignatian method, in societies such as the Aa (q.v.), Christian Friendship (q.v.), the Priestly (q.v.) and Catholic (q.v.) societies, and finally in the Congregation of the Oblates of Mary the Virgin (q.v.), of which he was Superior General from 1817 and which he definitively reconstituted with papal approval in 1825. During the imprisonment of Pius VII at Savona he was one of the most active organisers of secret assistance to the Pope, an activity which earned him confinement in his country house at Bardassano by the Napoleonic police (1811–14). After the Restoration he returned to Turin, where he sought to revive his former apostolic works: it was in this period that he made attempts to found the Ecclesiastical College (q.v.), which was later realised by the theologian L. Guala (q.v.). Lanteri’s contribution to the renewal of the formation of the clergy of the Subalpine region was of primary importance; in this regard he employed two highly effective means: the Spiritual Exercises according to the method of St Ignatius and the dissemination of the ascetical and above all moral works of St Alphonsus, of whom he was, in his time in Piedmont, the most ardent champion. His cause of beatification is under way.
Works. - Lanteri committed only a few writings to print; the majority of his works are preserved in manuscript form in the general archives of the Congregation of the Oblates of Mary the Virgin. Various apologetic writings or those concerning specific dogmatic or moral topics (for example, the organic articles of 1802, the imperial catechism, the four Gallican articles, the conciliabulum of 1811, the so-called Concordat of Fontainebleau, the treatise De gratia by the Jansenist Salina, etc.) were circulated in manuscript copies to avoid police harassment. By temperament, influenced by the grave political and religious situation in Piedmont at the end of the 18th and the beginning of the 19th century, Lanteri consistently preferred anonymity. The following anonymous works belong to him: Réflexions sur la sainteté et doctrine du bienf. Liguori (Lyon–Paris 1823, translated into Italian, Reggio 1825 and reprinted several times with modifications); Réponse à la question si la doctrine du bienf. Liguori est toute sûre et approuvée par le St-Siège (Lyon 1824); Esercizi spirituali di s. Ignazio di Lojola col direttore del buon uso de’ suddetti Esercizi ed alcune notizie intorno ad essi (Turin 1829; to which should be added the posthumous edition of the Medulla libelli Exercitorum s. Ignatii, published as an appendix to the Directory of the Oblates of Mary the Virgin, Turin 1854, pp. 189–218).