Geoffroy d'Harcourt was the youngest son of John III d'Harcourt, Viscount of Châtellerault and Saint-Sauveur, and Alix de Brabant, the daughter of Godfrey of Brabant. Harcourt was known as "the lame" due to him having a deformed leg, which made him limp. He was knighted in 1326 and inherited the Viscounty of Saint-Sauveur in 1330. In 1339, along with his older brother John IV of Harcourt, he became one of the 50 main Norman barons who pledged to help the King Philip VI of France in a future invasion of England. This attempt came to an end in 1340 with the annihilation of the French fleet during the Battle of Sluys, at the end of the Flanders campaign to which Geoffroy d'Harcourt participated with 6 knights and 30 squires.