Anglo-Norman Cluniac monk who became bishop of Hereford and later of London; he was an unsuccessful rival of Thomas Becket (Becket, Saint Thomas) for the archbishopric of Canterbury and afterward was Becket's opponent in ecclesiastical and secular politics.

Gilbert's appointment in 1139 as abbot of Gloucester was confirmed by King Stephen of England, although both previously and subsequently Gilbert supported the claim of Matilda, daughter of King Henry I, to the English throne. Still later he took the side of Henry II, son of Matilda and successor to Stephen, in the long conflict that ended in Becket's murder. Nominated to the see of Hereford in 1148, he hoped to succeed Archbishop Theobald of Canterbury (died 1161), but the King chose Becket, who also was royal chancellor and, at that time, a close friend of Henry. In 1163 Becket procured for Gilbert the see of London, but Gilbert evaded the profession of obedience to Becket as primate of the English church, apparently aspiring to make his see independent of Canterbury. On the questions of lay and ecclesiastical jurisdiction raised by the Constitutions of Clarendon (January 1164), Gilbert agreed with the views of the King, whose confessor he had become. When Becket rejected his advice to yield, Gilbert encouraged the other English bishops to repudiate the Archbishop's authority. During Becket's exile in France, Gilbert skillfully prevented Pope Alexander III from supporting Becket wholeheartedly, but he also restrained Henry from an open conflict with the papacy.

Gilbert was one of the bishops excommunicated (Dec. 25, 1170) by Becket for participating in the coronation of Henry's son, Henry the Young King (June 1170), by the Archbishop of York; he had no part in the murder (December 29) of the Archbishop by some of the King's household knights. His remaining years were uneventful.