He was "surnamed Crispin, earl of Brionne, in Normandy." He succeeded his father at Brionne as well as at Eu. However, after the death of his father, Godfrey, count of Eu, he soon quarrelled with his uncle, duke Richard II, and was deprived of his patrimony. Eu was given to William, another of duke Richard II's bastard sons, and Gilbert was left with only the lordship of Brionne. He afterwards regained his position, and in the reign of duke Robert was in high favor at court, when the castle of Brionne was restored to him. Gilbert assumed the title of count of Brionne while not relinquishing his claim to Eu, but the county of Eu had been in the meanwhile given away by duke Richard II to another member of the family, and neither Gilbert nor his descendants ever recovered possession of Eu. Even so, when count William of Eu died shortly before 1040, Gilbert assumed the land and title. Gilbert was selected in 1035, when duke Robert was starting for the Holy Land, to be one of the guardians of the young count
William, and for the next five years he was one of the most powerful nobles in Normandy. His duty to his ward was not unfaithfully discharged, but he abused his position to plunder the orphan heirs of his neighbour the sieur de Montreuil, and in revenge the "sons of Giroie" cruelly murdered him in 1040, as he was riding peaceably on his mule near EchaufrŽ "expecting no evil." His cruel death caused his faults to be forgotten, and King William retained to the last a kindly recollection of his guardian. When the King on his death bed was recounting the horrors of his early life, he mentioned count Gilbert, "the father of his country," among the pillars of the state who were perfidiously murdered by his enemies. After Gilbert's assassination in 1040, his young sons, Richard and Baldwin, were forced to flee Normandy, finding safety at the court of Baldwin V, count of Flanders. When William the Conqueror married count Baldwin's daughter, he restored Richard and Baldwin to Normandy, but he did not invest them with either Brionne or Eu or a comital title. William granted the lordships of Bienfaite and Orbec to Richard. Although Gilbert's descendants later pressed a claim for Brionne, it was never restored.
Count Gilbert probably married a relation of the count of Flanders, for his infant sons Richard and Baldwin were taken after his death to that country, and were brought up under the protection of count Baldwin. They returned to their native country when William of Normandy married Matilda of Flanders, and by count Baldwin's intercession were reinstated in as much of their father's fief as had not been otherwise disposed of. Richard now obtained the fiefs of Bienfaite and Orbec, and after the conquest of England received Tonbridge Castle in Kent as compensation for his hereditary claims to the castle of Brionne. At the same time Meules and Sap were given to Baldwin for his share, and he was allowed to marry the King's cousin. His wife, Albreda, was a granddaughter of duke Richard II, and was probably a sister of Guy of Burgundy, the rebel constable of Brionne Castle, who was exiled from Normandy in 1050. Richard and Baldwin were afterwards conspicuous in the conquest of England, and were not forgotten in the division of the spoil. They both founded powerful families, and Richard was the ancestor of the great house of Clare.