William Alnwick was Bishop of Norwich (1426-1436) and later (1436-1449) of Lincoln.

He was a monk of St. Alban's and in the confidence of Henry V. Henry VI made him his confessor and keeper of the privy seat. He was educated and enjoyed a great reputation for sanctity and orthodoxy.

He prosecuted very vigorously the heretic Lollards. Alnwick had an influence in the great scholarly foundations of Henry VI and occupied himself in restoring Lincoln Cathedral.

In 1425 he was recommended by the King of England to the Holy See for the Bishopric of Ely.