After becoming an experienced seaman, he went on a French mission to the king of Siam, whom he served as grand admiral for two years (1685–87). Returning to France as commandant of a frigate stationed at Dunkirk, Forbin was captured by the English but managed to escape. Early in the War of the Spanish Succession (1701–13) his squadron in the Adriatic cut the supply line of the imperial forces in Italy. Forbin was transferred to the northern squadron, where he played havoc with the Dutch Baltic convoy off the Dogger Bank in October 1706. He seized 22 English merchantmen and 2 men-of-war the following May and captured 34 ships of the Dutch Muscovy convoy in June. He resigned from the navy following his failure to carry out an expedition that was to transport James the Old Pretender, claimant to the English throne, to Scotland in 1708.