Baldwin was later declared legitimate by the pope, at the instigation of King Louis IX of France.
He fought his whole life, together with his brother John I, against his half-brothers from his mother's second marriage with William II of Dampierre.
He was said to be responsible for the accident that killed his half-brother William III of Dampierre during a tournament in Trazegnies.
After the Edict of Péronne and the death of his brother John, he reconciled with his mother, who sent him to Namur on a revenge expedition.
[2] In 1243, Baldwin married Felicitas (1220-1307), the daughter of Thomas II of Coucy, Lord of Vervins.