He was the third son of Geoffrey de Mandeville, 1st Earl of Essex and Rohese de Vere. William grew up at the court of the Count of Flanders. On the death of his elder brother Geoffrey in 1166 he became Earl of Essex, and returned to England, were he spent much time at the court of Henry II. He stayed loyal to the king during the 1173 rebellion of the king's sons.
In 1177 he became a crusader, in company with a companion of his youth, Philip of Flanders. The two fought at the Battle of Ramlah. William returned to England in the fall of 1178.
In 1180 he married Hawise, daughter and heiress of William, count of Aumâle, who had died the previous year. He gained possession of her lands, both in Normandy and in England, along with the title of Count of Aumâle (or Earl of Albermarle as it is sometimes called).
William fought in the wars against the French towards the end of Henry II's reign, and was with the king at the end of his life in 1189.
He carried the crown at the coronation of Richard I, and retained his place in the new court. Richard appointed him one of the two chief justiciars of England. But William died a few months later.
| Preceded by: Geoffrey de Mandeville | Earl of Essex | Followed by: Extinct |