Guillaume of Jumièges records that "secundus Willelmus de Warenna comes Surreiæ...tertius Willelmus filius eius" was born to "Elizabeth filia Hugonis Magni comitis Viromandorum", who had first married "Roberto comiti Mellenti" by whom she had "tres filios et totidem filias". William de Garenne donated property to St Faith, Longueville by charter dated to , witnessed by "Ysabel comitissa uxor comitis et Willelmo et Radulfo filii eorum". "W comes de Warenna et Isabella comitissa uxor mea necnon filii nostri Willelmus…et Radulfus" donated property to Castle Acre Priory by undated charter.
He succeeded his father in 1138 as Earl of Surrey. An undated charter of "Johannes comes Warennæ" confirmed earlier donations to Thetford Priory by "Willielmus comes Warenniæ" for the souls of "Willielmi comitis patris mei…matris meæ Isabellæ et fratrum meorum Radulphi Warenniæ et Reginaldi Warenniæ".
Robert of Torigny records that "tercii Willermi comitis de Guarenna" accompanied Louis VII King of France to Jerusalem and died there. William of Tyre records "comes Guarenna...Galcherius de Montiay, Evrardus de Bretol, Berus de Magnac…" among those killed in battle at Laodicea, in early 1148 (N.S.). 1
1st son and heir, was born probably in 1119. In June 1137 he was one of the nobles who deserted Stephen's army in Normandy. The King pursued them to Pontaudemer, where he held William de Warenne junior and other youths and did his best to pacify them; but did not dare to make them fight. He was with his half-brother Waleran, Count of Meulan, at Rouen on 18 Dec. 113 8, and at Oxford in 1139 or early in 1140. On 2 February 1140/1 he was in Stephen's army at the battle of Lincoln, and with Waleran fled before the enemy's opening charge. However, the brothers soon rallied to the Queen and were with her in London about June 1141. After the King's release on 1 November he witnessed royal charters at Canterbury at Christmas 1141 and at Ipswich early in 1142. On Palm Sunday, 24 March 1145/6, he took the cross, and in June 1147 he set off on crusade. He was a benefactor to the priories of Lewes, Castle Acre, Nosteil and Thetford, the Templars and St. Mary's Abbey, York. He married Ela or Ala, daughter of William TALVAS, COUNT OF PONTHIEU (son of Robert DE BELLÊME, 3rd EARL OF SHREWSBURY), by Ela, widow of Bertrand, COUNT OF TOULOUSE, and daughter of Eudes BOREL, DUKE OF BURGUNDY. He died s.p.m. 19 January 1147/8, being slain when the rearguard of the French King's army was cut to pieces in the defiles of Laodicea (i). His widow married, probably in or before 1152, Patrick (DE SALISBURY), 1st EARL OF WILTSHIRE or SALISBURY (died 1168). She is said to have died 4 October 1174.
(i) He left an only daughter and heir Isabel. He was probably the first to assume the checkered shield of gold and azure, differenced by the change of colour from the checkered shield borne by his half-brother Waleran, Count of Meulan. 2