Son of Reginald de Braose and Gracia de Briwere, a scion of the Marcher lords. His grandmother and uncle were starved to death on the orders of King John in 1210. He married Eve Marshal, daughter of the famous William Marshal, and they had four daughters.
William is best known as the lover of Joan, King John's illegitimate daughter and the wife of Llywelyn Fawr. Llywelyn caught them in his bedchamber and had William hanged. Sharon Kay Penman's novel "Here Be Dragons" is partly about William and Joan.