 Billot did pastoral work in Paris from 1875 to 1878 and in Laval until 1879.He taught at the Catholic University of Angers from 1879 to 1882 and made his final vows as a Jesuit on 2 February 1883, while teaching at the Jesuit Scholasticate on Jersey.In 1885, Billot became a professor of dogmatic theology at the Pontifical Gregorian University in Rome.