William Sharington was the son of Thomas Sharington and his wife Katherine Pyrton. Little is known of his early life. His family was wealthy and owned several manors. They came from Norfolk.
He married three times: first to Ursula, the illegitimate daughter of John Bourchier, 2nd Baron Berners. His father in law was influential and it is probably because of him that Sharington became well placed in the King’s court: in 1538, he was in the retinue of the diplomat and Chief Gentleman of the Privy Chamber, Sir Francis Bryan, who was a nephew of Lord Berners. He then became a Page of the Robes and a Groom by 1540. In 1541 he was elevated to the Privy Chamber.