Tromelin joined the navy as a Garde-Marine on 6 July 1750. On 11 October 1755, he was promoted to ensign. He served on the 22-gun frigate Hermine from 7 December 1760 to 26 November 1761 under Lieutenant Toussaint Julien Auffray du Guélambert, taking part in the Battle of Cape Finisterre on 13 and 14 August 1761.
