The illegitimate son of the elector Frederick Augustus I of Saxony (later also King Augustus II of Poland), young Maurice was sent by his father to serve under Prince Eugene of Savoy against the French in Flanders in 1709–10. In 1711 he was made Graf von Sachsen (count of Saxony; in French, comte de Saxe). His father bought him a German regiment in the French service in 1719, and Saxe quickly won recognition for his innovations in military training, especially in musketry.

Anna Ivanovna, duchess of Courland (later empress of Russia), secured Saxe's election as duke of Courland (a Baltic duchy between Prussia and Latvia) in 1726, but the Russians expelled him from the region in 1727 in order to prevent him from marrying the duchess. Returning to France, Saxe in 1732 wrote Mes Rêveries (published in 1756–57), a remarkably original treatise on the science of warfare. He served with distinction in the French army against his own half brother, King August III of Poland, in the War of the Polish Succession (1733–38) and in 1734 was made a lieutenant general.

In November 1741, six months after France joined Prussia against Austria in the War of the Austrian Succession, Saxe invaded Bohemia and captured Prague. Although the British had not yet become involved in the conflict, the French king Louis XV in January 1744 made Saxe commander of a force that was to invade Great Britain on behalf of Charles Edward, the Young Pretender, the Stuart claimant to the British throne. The project was dropped after a storm shattered Saxe's invasion fleet at Dunkirk in March. Shortly thereafter, Louis formally declared war on Great Britain and promoted Saxe to the rank of marshal. Saxe and the king then invaded the Austrian Netherlands.

The king wisely allowed Saxe to give the orders in the ensuing campaign. Their forces surrounded Tournai, and, when allied troops advanced from the east to relieve the siege, Saxe decisively defeated them in the Battle of Fontenoy (Fontenoy, Battle of) (May 11, 1745). It was France's last great victory before the outbreak of the French Revolution in 1789. Saxe then captured Brussels and Antwerp (February 1746). Turning south, he seized Mons and Namur, and on Oct. 11, 1746, he defeated the allies at Raucoux, near Liège, thereby completing the conquest of the Austrian Netherlands.

In January 1747 Louis appointed Saxe marshal general of France. In 1747 he invaded Holland, defeated an allied army in the Battle of Lauffeld near Maastricht (July 2), and captured the fortress of Bergen-Op-Zoom. Saxe retired to his château at Chambord, where he died. His grandson was the father of the novelist George Sand.