Baldwin was the son of BaldwinV of Hainaut, and Margaret I, sister of Philip of Alsace and Countess of Flanders.
Baldwin took possession of a much-reduced Flanders, for his uncle had given a large chunk, including Artois, as dowry to Baldwin's sister Isabelle of Hainaut on her marriage to King Philip II of France, and another significant piece to his own wife.
Baldwin's uncle William of Thy (an illegitimate son of Baldwin IV of Hainaut) was regent for Hainaut.
Philip of Alsace was count of Flanders from 1168 to 1191.
Margaret II of Flanders (1202-1278) was countess of Flanders from 1244 to 1278 and countess of Hainaut from 1244 to 1246.
Crusades BaldwinV of Hainaut (1150-December 17, 1195) was count of Hainaut (1120?_1195), count of Flanders as Baldwin VIII (1191-1195) and margrave of Namur as Baldwin I (1189-1195).