In January 1361, Edward III and John II of France jointly to petitioned Pope Innocent VI, to make William a canon at Lincoln Cathedral.

For instance, in April 1363, Edward III presented him to the archdeaconry of Lincoln, a move that was approved by Pope Urban V in November 1363 only after representations from Sir Nicholas de Loveyne, the king's ambassador to the papal court.

William had shown considerable talent as an administrator and in June 1363 was appointed Lord Privy Seal[3] and then in October 1366 he was elected Bishop of Winchester,[4] Pope Urban V approved his appointment in July 1367, and he was consecrated at St Paul's Cathedral in London on 10 October 1367[5] and enthroned at Winchester Cathedral in July 1368.

He remained politically important, and was one of four bishops appointed to the new royal council in May 1376 after Latimer was impeached during the Good Parliament.

Latimer was pardoned by king in October 1376, and William found himself charged with financial irregularities and mismanagement towards the end of the year.

He was banished from court and the income from his church properties was seized in late 1376, but he was pardoned by the new king Richard II in July 1377, weeks after Edward III died.

The funds to endow the colleges, and pay for the building works, came from William's lucrative church positions, discounting of exchequer tallies (that is, speculation on tax revenues due to the king), exporting wool, and using his influence to obtain papal approval for the acquisition of the income of the "alien priories" that belonged to monasteries in France, which were confiscated by the crown during the Hundred Years' War.

William was concentrating on his foundation by the time Henry IV deposed Richard II in 1399, but he welcomed the new king in Winchester in 1400.

William died at Bishop's Waltham in Hampshire on 27 September 1404 and was buried in his chantry chapel on the south side of the nave in Winchester Cathedral.