| Philippe Henri de Ségur | |
| Successor1: | Louis Charles Auguste Le Tonnelier, Baron de Breteuil, Baron de Preuilly |
| Birth Place: | Paris, Isle-de-France, Kingdom of France |
| Birth Date: | 20 January 1724 |
| Battles: | Seven Years' War |
| Honorific Suffix: | Marquis de Ségur |
| Honorific Prefix: | Maréchal de France |
| Serviceyears: | 1739–1787 |
| Predecessor1: | Charles Gravier, Comte de Vergennes |
| Office: | Marquis of Ségur |
| Term1: | 23 December 1780 – 27 August 1787 |
| Office1: | Secretary of State for War |
| Term: | 19 June 1751 – 3 October 1801 |
| Succeeded: | Louis-Philippe, Marquis de Ségur |
| Predecessor: | Henri François, Comte de Ségur |
| Caption: | Official portrait as Marshal of France by Élisabeth Vigée Le Brun in 1789 |
| Death Place: | Paris, Seine-et-Marne, French Consulate |
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. He was wounded at Roucoux in Flanders in October 1746, and lost an arm at Lauffeld in 1747. 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.
During the Seven Years' War he fought at Hastenbeck (1757), Krefeld (1758) and Minden (1759). In 1760 he was taken prisoner at Kloster Kampen.
The ability which he showed in the government of Franche-Comté in 1775 led in 1780 to his appointment as Minister for War under Necker. 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. On 13 June 1783 he became a marshal of France. He resigned from the ministry of war in 1787.
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. He died in Paris the next year.
Ségur married in Paris on 3 February 1749 Louise Anne Madeleine de Vernon (Paris, 1729 – Paris, 12 March 1778), daughter of Alexandre de Vernon and Anne du Vivier, and had two sons: