Kersaint joined the Navy as a Garde-Marine in February 1722, and was promoted to Ensign in October 1731, Lieutenant in May 1741, and Captain in January 1747.[1]
In 1756, he took command of the 74-gunIntrépide. He led a division to cruise off Guinea, destroying British factories and engaging in commerce raiding. He then sailed to the Caribbean. On 21 October 1757, near Caicos, he encountered three British ships, leading to the Battle of Cap-Français. Kersaint was wounded and Intrépide was almost completely dismasted, but she managed to repel the British.[1]
In 1759, he took command of Thésée. He took part in the Battle of Quiberon Bay on 20 November 1759. During the battle, as Kersaint was attempted to come to the aid of Conflans, Thésée performed a turn without closing her lower gunports. Water rushed into the gundeck,[1] and Thésée capsized, killing most aboard.[2]