William VI of Saint Omer was the castellan of Saint-Omer and lord of Fauquembergues briefly in ca.
The genealogist Baldwin of Avesnes records him as a son of William V of Saint Omer, but Arthur Giry has him rather a younger brother of the latter, i.e. he was one of the eleven children of William IV of Saint Omer and Ida of Avesnes.
[2] He succeeded his brother sometime between March 1246 and his own only attestation as castellan, in August 1247.
Very little is known of his tenure, which apparently was very brief; Baldwin of Avesnes merely records that he went on Crusade, where he died.
He was succeeded by his eldest sister Beatrice and her son William of Renenghes by 1251.