Mortemart joined the Navy as a Garde-Marine in 1771.[2] He took part in the several cruises with the escadre d'évolution, and was promoted to Lieutenant March 1779.[3]
In 1779, Mortemart was given command of the 26-gun frigate Aigrette, part of the squadron under Orvilliers. He then transferred to Diligente, on which he captured two British ships[2] and took part in the Battle of Fort Royal on 29 April and 30 April 1781.[4][5][6]
Mortemart was given command of Richemond, which he captained at the Battle of the Saintes in 12 April 1782, where she attempted to tow Glorieux to safety before being ordered to retreat.[2]
Mortemart was then tasked with bringing the news of the battle to Versailles. He was then promoted to Captain, aged just 25, and given command of the 40-gun frigate Nymphe, to cruise off Martinique with the 32-gun Amphitrite.[2] On 17 February 1781, they captured the 44-gun HMS Argo off Tortola.[8] The 74-gunHMS Invincible recaptured Argo shortly afterwards.[2]
Mortemart died of a sudden illness on 17 March 1783.[2]
Roche, Jean-Michel (2005). Dictionnaire des bâtiments de la flotte de guerre française de Colbert à nos jours. Vol. 1. Group Retozel-Maury Millau. ISBN978-2-9525917-0-6. OCLC165892922.