William de Longchamp (died 1197) was a medieval Lord Chancellor, Chief Justiciar, and Bishop of Ely in England. Born to a humble family in Normandy, he owed his advancement to royal favour. Although contemporary writers accused Longchamp's father of being the son of a peasant, he held land as a knight. Longchamp first served Henry II's illegitimate son Geoffrey, but quickly transferred to the service of Richard I, Henry's heir. When Richard became king in 1189, Longchamp paid £3,000 for the office of Chancellor, and was soon named to the see, or bishopric, of Ely and appointed legate by the pope.