He was the son and heir of Patrick of Salisbury, Earl of Wiltshire, styled Earl of Salisbury, and Adela of Ponthieu, Countess of Surrey.
[1] He married Eléonore, daughter of Robert III de Vitré, Baron of Vitré in Brittany, who died without male issue in 1196.
William bore the golden sceptre at the coronation of King Richard I, but the next year when the king became a prisoner by Emperor Henry VI, he was one of those who adhered to the then-count of Mortain, who later became King John of England.
In 1194 he served as High Sheriff of Somerset and Dorset.
In 1195, William was back with King Richard in the expedition into Normandy and upon his return to England was one of Richard's great council assembled at Nottingham.