William Petre was born in 1505 and educated at Exeter College, Oxford. He became a public servant, probably through the influence of the Boleyns, one of whom he had tutored at Oxford and another of whom was married to the king. He rose rapidly in the royal service and, in 1543, was knighted.

Petre was adept at sidestepping the great religious controversies of the day and held high office through the reigns of Henry VIII, Edward VI, and Mary I. He retired a rich man in 1557 to Ingatestone, a village in Essex, where he built a fine house with money derived from the dissolution of the monasteries. He died in 1572. Sir William's son John was created Baron of Writtle in 1603. Despite the origin of the family fortune, the later Lords Petre have mostly been Catholics. Their name is pronounced "Peter".