 He attended the seminary in Tortona, and was ordained to the priesthood on 8 November 1891.He then went to Rome, where he studied at the Pontifical Gregorian University and the Pontifical Lombard Seminary, alongside Luigi Sincero and Mario Nasalli Rocca di Corneliano.Upon returning to Tortona, Perosi undertook his pastoral ministry, also serving as a diocesan official and professor and vice-rector at its seminary.