Weygand was born in Brussels, Belgium. Some sources say that he was the illegitimate son of Empress Carlota of Mexico, which Weygand refused to either confirm or deny. He was educated in Marseilles and Paris before joining the military academy at Saint-Cyr, graduating in 1887 and was posted to a cavalry regiment. He was then an instructor at Saumur. At the outbreak of WW I he was a Lieutenant-Colonel on the staff of Joseph Joffre but in August 1914 he became chief-of-staff to Ferdinand Foch. He was promoted to Brigadier General in 1916 and Major General in 1918, serving on the War Council from 1917. He remained on the staff of Foch when Foch was appointed Supreme Allied Commander. In 1918 he served on the armistice negotiations and actually read them out to the Germans at Compiegne, in the famous railway carriage.
After the war his career continued well despite the disgrace of Foch. Weygand was briefly sent as an advisor to Poland in 1920 during Polish-Soviet war, trying without much success to aid Josef Pilsudski. He also served as high commissioner in Syria and as Inspector-General of the army from 1931 before retiring in 1935.
Weygand was recalled to active service by Edouard Daladier in August 1939 to head the French forces in the Middle East. By May 1940 the military disaster in France was such that the Supreme Commander, Maurice Gamelin, was dismissed and Weygand was recalled to replace him. He arrived on May 17 and after an abortive attempt to hold the German advance he became in favour of an armistice by mid-June.
In the new Vichy cabinet, he was made Minister for National Defense for three months and then Delegate-General of the North African colonies. His anti-German actions led to his recall and dismissal in November 1941; one year later, in November 1942, following the Allied invasion of North Africa, Weygand recommended that France resume the war against Germany and was promptly arrested. He remained imprisoned until May 1945 when he was liberated by the Americans. Returned to France, he was held as a collaborator at the Val-de-Grâce but finally was released in May 1946 and cleared in 1948.