The abbey was founded on the banks of the Aa in the 7th century by Bishop Audomar of Thérouanne, who is now better known as Saint Omer.

He sent the monks Bertin, Momelin, and Ebertram from Sithiu (now St-Omer) to proselytize among the pagans in the region.

Its importance rested in no small part on having the body of Silvin of Auchy, whose body had been stolen by Arnulf I and moved to Saint-Bertin; he, along with the saints Folcwin, Bertin, and Winnoc were essential to the foundational identity of the abbey.

The reference to the theft of Silvin's body was whitewashed: a twelfth-century copy of Folcwin's Gesta abbatum Sancti Bertini, "Deeds of the Abbots of Saint-Bertin", makes no mention of it.

The buttress they erected to support it is still visible, although the tower itself collapsed in 1947 owing to damage sustained in the shelling of the town during World War II.