William was a son of Rodulf or Ralph de Warenne[1] and Emma and reported to have descended from a sibling of Duchess Gunnor, wife of Duke Richard I.

Associations with the village of Vascœuil led to identification of the Warenne progenitrix with a widow Beatrice, daughter of Tesselin, Viscount of Rouen, who appeared there in 1054–1060.

[2] [a] William was from the hamlet of Varenne, near Arques-la-Bataille, Duchy of Normandy, now in the canton of Bellencombre, Seine Maritime.

[12] At about the same time he acquired lands at Bellencombre including the castle that became the centre of William de Warenne's holdings in Normandy.

[16][17][18] He fought against rebels at the Isle of Ely in 1071, where he showed a special desire to hunt down Hereward the Wake, who had killed his brother-in-law Frederick the year before.

[26] In the Rebellion of 1088 he was mortally wounded at the First Siege of Pevensey Castle, and died on 24 June 1088 at Lewes, now in East Sussex.

[27][28] William de Warenne married first, before 1070, Gundred, Countess of Surrey,[29][30] sister of Gerbod the Fleming, 1st Earl of Chester.