William de Warenne, 2nd Earl of Surrey (d. 1138), was the son of William de Warenne, 1st Earl of Surrey and his first wife Gundrada. He is more often referred to as Earl Warenne or Earl of Warenne than as Earl of Surrey.

Sometime around 1093 he tried to marry Matilda (or Edith), daughter of king Malcolm III of Scotland. She instead married Henry I of England, and this may be the cause of William's great dislike of Henry I, which was to be his apparent motivator in the following years.

He accompanied Robert Curthose in his 1101 invasion of England, and afterwards lost his English lands and titles and was exiled to Normandy. There he complained to Curthose that he expended great effort in the duke's behalf and had in return lost nearly everything. Curthose's return to England in 1103 was apparently made to convince his brother to restore William's earldom. This was successful, though Curthose had to give up what he had received after the 1101 invasion, and subsequently William was loyal to king Henry.

To further insure William's loyalty Henry considered marrying him to one of his many illegitimate daughters. He was however disuaded by Archbishop Anselm of Canterbury, for any of the daughters would have been within the prohibited degrees of consanguinity. The precise nature of the consanguinous relationship Anselm had in mind has been much debated, but it is most likely he was referring to common descent from the father of duchess Gunnor.

William was one of the commanders on Henry's side (against Robert Curthose) at the Battle of Tinchebray in 1108. Afterwards, with his loyalty thus proven, he became more prominent in Henry's court.

In 1110 Curthose's son William Clito escaped along with Helias of Saint-Saens, and afterwards Warenne received the forfeited Saint-Saens lands, which were very near his own in upper Normandy. By this maneuver king Henry further assured his loyalty, for the successful return of Clito would mean at the very least Warenne's loss of this new territory.

He fought at the Battle of Bremule in 1119, and was at Henry's deathbed 1135.

In 1118 William acquired the royal-blooded bride he desired when married Elizabeth (Isabelle) de Vermandois. She was a daughter of count Hugh of Vermandois, a son of Henry I of France, and was the widow of Robert de Beaumont, 1st Earl of Leicester.

By Elizabeth he had 3 sons and 2 daughters:
• William de Warenne, 3rd Earl of Surrey;
• Reginald de Warenne, who inherited his father's property in upper Normandy. He married Adeline, daughter of William, lord of Wormgay in Norfolk, by whom he had a son William, whose daughter and sole heir Beatrice married first Dodo, lord Bardolf, and secondly Hubert de Burgh;
• Ralph de Warenne
• Gundrada de Warenne, who married first Roger de Beaumont, 2nd Earl of Warwick, and second William, lord of Kendal, and is most remembered for expelling king Stephen's garrison from Warwick Castle;
• Ada de Warenne, who married Henry of Scotland, 3rd Earl of Huntingdon