He succeeded his father,
William, sometime before 1129, possibly as early as 1116. A key portion of the family patrimony in Essex was in the King's hands. William had incurred a debt to the crown, perhaps in part due to a large fine levied in 1101 by
Henry I due to his displeasure at the escape of the important political prisoner
Ranulph Flambard while William was in charge of the
Tower of London. The King also held the substantial estate of Geoffrey's maternal grandfather
Eudo le Dapifer to which Geoffrey laid claim. Geoffrey gained Eudo's lands and his father's offices during the shifting tides of fortunes of the two competitors for the English throne after Henry I's death in 1135. He initially supported
Stephen, who sometime in 1140 (most likely May of that year) made him
Earl of Essex. By 1140 or 1141, King Stephen had returned to him the lucrative manors in Essex. He founded a Benedictine priory (later
Walden Abbey) at
Walden, Essex and constructed a castle there. He also contributed to
Hurley Priory in Berkshire, which had been founded by his grandfather
Geoffrey de Mandeville I. After the defeat and capture of Stephen at
Lincoln early in 1141, Earl Geoffrey, like many barons, acknowledged Stephen's rival
Empress Matilda as his sovereign lady. She confirmed his custody of the Tower, forgave the large debts his father had incurred to the crown, granted him the
Norman lands of Eudo
le Dapifer, and appointed him
Sheriff of Essex and Hertfordshire,
Middlesex and
London. When Stephen was released in December of that year, Earl Geoffrey returned to his original allegiance. There has been much scholarly debate over the dating of the charters he received from King Stephen and Empress Matilda. Depending on the order and timing of those documents, either Geoffrey appears to have been playing off one against the other to get what he wanted or his support was courted by the rival claimants to the throne. The king arrested the earl in 1143 and, threatened with execution, Geoffrey surrendered his castles of
Pleshey and
Saffron Walden as well as custody of the Tower of London to Stephen. In reaction, Earl Geoffrey launched a rebellion. ==Outlaw activity and death==