Son of the public prosecutor of the parlement of Bourgogne, Languet de Gercy was a protégé of Jacques Bénigne Bossuet.

Languet de Gercy was the general vicar of the diocese of Autun, which includes the parish of Paray-le-Monial where Saint Marguerite Marie Alacoque is buried.

Languet de Gergy's work on the life of Alacoque was violently attacked by the Jansenists opposed to the Catholic devotion of the Sacred Heart.

He belonged to the parti des dévots opposed to the philosophies of the Age of Enlightenment and fought fiercely against the candidacies of Montesquieu and Voltaire to l'Académie française.

In addition to his treatises and religious pamphlets, Languet de Gergy was the author of books on the Divine Office, catechism, and of pastoral letters.