Sir William was the son of  John Norreys of Fifield House, in the parish of Bray in Berkshire, and his wife, Mary the daughter of William Staverton of Stroud Hall, also in Bray. He must be carefully distinguished from his contemporary, William Norreys (1548-1579) of Rycote in Oxfordshire, whose grand-uncle, Sir John Norreys, had also held a manor in Bray parish, at Ockwells; and also from William Norreys of Speke Hall in Lancashire. All three were distant relatives.

At the age of twenty-one, William was admitted to Gray's Inn and, by 1553, had become a Gentleman Usher of the Privy Chamber. He was dropped from office when Queen Mary came to the Throne, but she later granted him his father's old offices of Steward of Foliejon Park (Winkfield) and Controller of Works at Windsor Castle and in the associated Great Park These were confirmed upon Queen Elizabeth's accession. Sir William became MP for Windsor in 1554, 1555 & 1558  and, in 1557, was sent, as a Royal Herald,  to France in order to declare war against King Henry II. He was also appointed steward of the Royal manors of Bray and Cookham, adjoining his home, in 1567, but quickly surrendered the manors to the Constable of Windsor Castle. Upon his father's death, in 1577, Sir William inherited, not only his property in Fifield, but his offices as Gentleman Usher of the Black Rod (Parliament House) and of the Most Noble Order of the Garter. He also became a Gentleman-Pensioner  and JP for Berkshire.