Sir Jean III de Grailly, Captal de Buch KG (d. Paris, September 7, 1376), son of Jean II de Grailly, Captal de Buch, Vicomte de Benauges, and Blanch de Foix, is a cousin of the Counts of Foix and a military leader in the Hundred Years' War who is praised by the chronicler Jean Froissart as an ideal of chivalry.

Attached to the English side in the conflict, he is made Count of Bigorre by Edward III of England, and is also a founder and the fourth Knight of the Garter in 1348.

He plays a decisive role as a cavalry leader under Edward, the Black Prince in the Battle of Poitiers(1356), with de Buch leading a flanking move against the French that results in the capture of the king of France (John II), as well as many of his nobles.

John is taken to London by the Black Prince and held to ransom.