Isabella was born in Valenciennes on 5 April 1170, the daughter of Baldwin V, Count of Hainaut, and Margaret I, Countess of Flanders.

She was a descendant of Charlemagne and the chroniclers of the time saw in this marriage a union of the Carolingian and Capetian dynasties, which was represented in her son Louis VIII.

[5] Though Isabella received extravagant praise from certain annalists, she initially failed to win Philip's affections owing to her inability to provide him with an heir, although she was only 14 years old at the time.

[6] Meanwhile, in 1184, Philip was waging war against Flanders; angered at seeing his wife's father Baldwin support his enemies, he threatened to divorce her.

[7] According to Gislebert of Mons, Isabella then appeared barefooted and dressed as a penitent in the town's churches, thus gaining the sympathy of the people.

[12] Owing to complications in childbirth, she died in Paris the next day, 15 March, aged not quite 20, and was buried in the cathedral of Notre-Dame.