In order to marry Agnes, Marie's father Philip had to get a divorce from his neglected second wife Ingeborg of Denmark.

Agnes gave birth to Marie and then to her brother, Philip I, Count of Boulogne.

Innocent III declared Philip's marriage to Agnes null and void, as he was still married to Ingeborg.

Marie's second betrothal was to Arthur I, Duke of Brittany,[5] who was fighting against John for the Kingdom of England.

The couple had two daughters: Marie died on 15 August 1224 and was buried at Affligem Abbey.