Walter was the son of Osbern de Bolbec, Lord of Longueville by a sister of
Gunnor, Duchess of Normandy. As such he was first cousin twice removed of
William the Conqueror. From the mid 1040s Walter's name appears among the loyal supporters of William the Conqueror. Walter was at the
Battle of Mortemer and was among the Norman barons who surprised and defeated Counts Odo and Renaud leading the French contingent attacking Normandy from the east. In particular, he and another great vassal
Robert of Eu encountered Odo's army encamped in the village of Mortemer with no sentries and the soldiers were drunk. The Normans attacked the French while they slept, most being either killed or taken prisoner, Like many other Norman and French knights during the eleventh and early twelfth centuries, Walter served as a Christian knight in Spain () against the Saracens. His
epithet de Barbastre was earned when he took part in the
Siege of Barbastro, an undertaking sanctioned by
Pope Alexander II against the Moors in 1064, one of the more famous exploits of that time. Walter went on pilgrimage to
Santiago de Compostela, after the siege of Barbastro and before returning to Normandy. After telling them of his plan to invade England and take the crown for himself they supported him fully but suggested he should call a meeting of all his vassals, which William did. Walter was one of two who, having been offered the privilege of carrying William's
standard in the battle, respectfully refused. Although by this time an older warrior with white hair, he wanted both hands free to fight. As a reward for his participation, Walter was granted the
feudal barony of Long Crendon, comprising 107 manors, 48 of which were in Buckinghamshire, of which the
caput was at
Long Crendon, Buckinghamshire. The date of his death is not recorded, but his son
Walter succeeded him before 1085. ==Family==