Walter was the son of Count Drogo of Vexin and Amiens and Godgifu, daughter of King Æthelred II of England.
He appeared in 1030 as a witness to a donation made by his father to the Abbey of Jumièges, and succeeded him in 1035.
He first attempted neutrality between the two, but ended up joining the camp of King Henry I in 1057.
Duke William began the conquest of Maine by taking the fortresses one by one and finally seizing Le Mans and capturing Walter and Biota.
[4] His cousin, Ralph IV of Valois, inherited the counties of Vexin and Amiens, with the exception of the towns of Pontoise and Chaumont-en-Vexin which the King of France had seized.