Born into an ancient noble family in Riez, Basses-Alpes (Alpes de Haute Provence), Henry César, marquis de Castellane Majastre, was a career officer in the French naval service, and appears to have descended from a family with long connections to the navy. Among his most important contributions, at least from the American standpoint, Castellane Majastre served in the French fleet that sailed to the aid of the Americans in March, 1781.
As commander of the 74-gun vessel Marseillais , Castellane Majastre sailed from Brest with the fleet of Admiral François Joseph Paul, comte de Grasse, on March 22, 1781, bound for Martinique, and he subsequently took part in the decisive campaign leading to the capture of Cornwallis' army at Yorktown, including the actions on the Chesapeake in September, 1781, and at Yorktown itself in October. The marquis was singled out by de Grasse for special commendation for his part at the Chesapeake Capes.
Returning to the West Indies in November, 1781, Castellane Majastre led the Marseillais into action during the Battle of the Saints in April, 1782, forming part of the escadre blanche et bleu during this French naval disaster. In May, 1782, he was reported at Saint Domingue as part of the fleet under the marquis de Vaudreuil, and although his whereabouts for the next seven years are uncertain, at some point he returned home to Riez, where he died on May 5, 1789.