She was heiress to her father's titles as Lady of Béthune, of Dendermonde, of Richebourg and of Warneton, as well as Advocatess of the Abbey of Saint Vaast at Arras, and the ruler of these states in 1248-1264.

Matilda, also referred to as Mathilde or Mahaut, was born about 1230, the first child of Robert VII, Lord of the castle and town of Béthune and Advocate of the Abbey of Saint-Vaast at Arras, who was a major landowner and one of the twelve peers of Flanders.

In recognition of this important match for his eldest daughter, Robert of Béthune endowed her with the major part of his lands and titles.

[1] In October 1245, she still under age and unmarried, he made her heir to the ancient lands of his ancestors outside Béthune, the Pays de l'Alleu in which he held power of life and death.

[1] Matilda died on 8 November 1264 and was buried in a tomb of black marble in the Chapel of Saint Hubert within the abbey church of Flines-lez-Raches, her husband being placed beside her later.