Philippe Henri, Marquis de Ségur (20 January 1724 – 3 October 1801) was a grandson of Philippe II, Duke of Orléans, nobleman, Marshal of France, and Secretary of State for War under Louis XV and later Louis XVI.

Born in Paris, son of Henri François, comte de Ségur and his wife Philippe Angélique de Froissy, Philippe Henri was appointed to the command of an infantry regiment at eighteen, and served under his father in Italy and Bohemia.

In 1748 he succeeded his father as lieutenant-general of Champagne and Brie; he also received in 1753 the governorship of the county of Foix.

He created in 1783 the permanent general staff, and made admirable regulations with regard to barracks and military hospitals; and though he was officially responsible for the reactionary decree requiring four quarterings of nobility as a condition for the appointment of officers, the scheme is said not to have originated with him and to have been adopted under protest.

During the Terror he was imprisoned in La Force, and after his release was reduced to considerable straits until in 1800 he received a pension from Napoleon.