Sir William Petre (c. 1505 – 1572) (pronounced Peter) was Secretary of State to three successive Tudor monarchs, namely Kings Henry VIII, Edward VI and Queen Mary I. He also deputised for the Secretary of State to Elizabeth I.
Educated as a lawyer at the University of Oxford, he became a public servant, probably through the influence of the Boleyn family, one of whom, George Boleyn, he had tutored at Oxford and another of whom was Queen Anne Boleyn, second wife of King Henry VIII. He rose rapidly in the royal service and was knighted in 1543.
Sir William Petre was adept at side-stepping the great religious controversies of the day; in January 1544 he was appointed Secretary of State. He navigated the ship of state through the rest of Henry's troubled reign, managing a smooth succession in 1547. He held high office throughout the reigns of Henry VIII, Edward VI, Mary I and Elizabeth I until, owing to ill health he retired a rich man to his manor of Ingatestone, in Essex, where he had built Ingatestone Hall. His son was John Petre, 1st Baron Petre of Writtle, raised to the peerage in 1603. The later Barons Petre have mostly been Roman Catholics.
The musician William Byrd wrote a Pavan and a Galliard for Sir William Petre, which were published as part of his Parthenia.