Pierre Julien Tréhouart (Port Louis, 27 November 1759 - Toulon, 9 May 1804) was a French navy officer.
Tréhouart joined the navy as a volunteer in 1775, and was promoted to officer in 1777. In 1779, he rose to lieutenant de frégate and served under Suffren, who commanded him, taking part in five battles on ships of the line, two isolated actions on frigates
Tréhouart was promoted to sub-lieutenant in 1786. In June 1792, he captained the chartered merchantman Chancelière de Brabant, ferrying troops from Lorient to Pondichery. He was promoted to lieutenant later the same year.
As a lieutenant, he captained the Cybèle during the Action of 22 October 1794; he was promoted to captain by governor Malartic after the battle, on 24 October 1794. In 1795, Cybèle was attached to the division under Sercey and took part in the Action of 8 September 1796, where he ordered a boat launched to tug the becalmed Cybèle into a position where she could rake HMS Victorious. Tréhouart was promoted to chef de division on 19 December 1797.
Tréhouart returned to France on Cybèle and arrived in Rochefort in the summer of 1801. He had been appointed to command the Formidable since 9 April 1801. He retained this command for one year before captaining the Neptune.
He was awarded the rank of officer in the Legion of Honour on 14 June 1804, after his death.