His studies included not only theology, in which he gave particular attention to the Fathers of the Church and the great Scholastics, but also classical and Italian literature.
Having been master of studies for some time at the convent of San Marco, Florence, he was called to Rome in 1732 as professor of theology at the College of St. Thomas Aquinas, the future Pontifical University of Saint Thomas Aquinas, Angelicum where he was also made prior.
He held this position for two years, after which he became the theologian of Cardinal Neri Corsini, nephew of Pope Clement XII.
In 1749 Benedict XIV made him "Magister Sacri Palatii", or papal theologian, and on 24 September 1759, Clement XIII created him cardinal priest of the title of San Sisto.
It only covered the period up until the end of the sixth century; the twenty-first volume, which Orsi had begun, was finished by his former pupil Giovanni Bottari (Rome, 1762).