William Longchamp (died 1197), chancellor of England and bishop of Ely, entered public life at the close of Henry II's reign as official to the king's son Geoffrey, for the archdeaconry of Rouen . Henry II, who disliked him, called him the son of two traitors. He soon deserted Geoffrey for Richard, who made him chancellor of the duchy of Aquitaine . He always showed himself an able diplomat.

He first distinguished himself at Paris, as Richard's envoy, when he defeated Henry II's attempt to make peace with Philip Augustus (1189). On Richard's accession William became chancellor of the kingdom and bishop of Ely. When Richard left England (Dec. 1189), he put the tower of London in William's hands and chose him to share with Hugh de Puiset, the great bishop of Durham, the office of chief justiciar . William immediately quarrelled with Hugh, and by April 1190 had managed to oust him completely from office. In June 1190 he received a commission as a papal legate from Pope Celestine II. He was then master in church as well as state. But his disagreeable appearance and manners, his pride, his contempt for everything English made him detested. His progresses through the country with a train of a thousand knights were ruinous to those on whom devolved the burden of entertaining him. Even John seemed preferable to him.

John soon returned to England; he and his adherents were immediately involved in disputes with William, who was always worsted. At last (June 1191) Geoffrey, Archbishop of York and William's earliest benefactor (the aforementioned son of Henry II), was violently arrested by William's subordinates on landing at Dover. They exceeded their orders, which were to prevent the archbishop from entering England until he had sworn fealty to Richard. But this outrage was made a pretext for a general rising against William, whose legatine commission had now expired, and whose power was balanced by the presence of the archbishop of Rouen , Walter de Coutances, with a commission from the king. William shut himself up in the Tower, but he was forced to surrender his castles and expelled from the kingdom. In 1193 he joined Richard in Germany, and Richard seems to have attributed the settlement soon after concluded between himself and the emperor, to his dearest chancellor. For the rest of the reign Longchamp was employed in confidential and diplomatic missions by Richard all over the continent, in Germany, in France and at Rome. He died in January 1197. His loyalty to Richard was unswerving, and it was no doubt through his unscrupulous devotion to the royal interest that he incurred the hatred of Richard's English subjects.