Before the death of his father, he was known at court as the duc d'Agénois. He entered the army at the age of seventeen, and at the age of nineteen was made colonel of the regiment of Brie. His marriage in 1740 with Louise Félicité de Brehan, daughter of the Comte de Plélo, coupled with his connection with the Richelieu family, gave him an important place at court.