He was the son of Alice de Beaumont (daughter of the 4th Earl) and William de Maudit, and so was the grandson of Waleran de Beaumont, 4th Earl of Warwick. His father was the Lord of Hanslope and hereditary chamberlain of the exchequer, a title that went back to another William Maudit who held that office for Henry I.
He adhered to Henry III in the wars with the barons. He was surprised in his own castle, Warwick Castle by John Giffard, the governor of Kenilworth Castle. The walls of the castle were destroyed and the countess taken prisoner to Kenilworth, and only released on payment of a ransom nineteen hundred marks.
William Mauduit made the inner ward in the northwestern corner of Portchester Castle (Portus Adurni) for an unknown reason.
This was made in 1090 and is a Norman Castle and had palisades on each side of the castle.
