He was born at Montigny-sur-Avre. His father was a member of the distinguished Montmorency family and his mother was a descendant of Rouen legal nobility. As early as age 8 it was decided that he would have a career in the Church. He studied at the Jesuit college at La Flèche, and then at Paris. He briefly interrupted his studies because of a family crisis but he was very soon ordained subdeacon in 1646 and a priest in 1647. While he was archdeacon of Évreux in 1648, he showed much passion for his work which made it clear that he would be a perfect fit for missionary work in Indochina.