His parentage is specified in the Cartulaire de Saint-Bertin. "…Baldwini filii Arnulfi marchysi…" signed the charter dated 8 Jul 941 under which "Arnulfus…regis…marchysus" restored property to Saint-Pierre de Gand. "Arnulfus Flandrie comes et marchisus" granted use of property "Snellenghem in pago Flandrensi" to Saint-Pierre de Gand, for "uxore mea…Adala atque…filio meo Balduino et filia mea Lietgardis" and for deceased "Balduino genitore meo et Elstrudis genetrice mea atque Heeberto filio meo", by charter dated 10 Jul 953.
He ruled with his father from 958 as BAUDOUIN III joint Count of Flanders and Artois, his father granting him the administration of the south of the county. A charter dated to 20 Jan [958/61] records the peace settlement agreed by "Baulduin…Marquis" between the abbey of Saint-Pierre de Gand and the avoués of Douchy, although this document is unlikely to be contemporary in the form shown in the compilation as it is written in old French.
The Annales Blandinienses record the deaths in 962 of "Baldwinus, filius Arnulfi marchisi, et soror eius Liutgardis". The Annales Egmundani record the death in 962 of "Baldwinus filius Arnulfi marchisi Flandrensium". 2
Also called Baudouin III, Comte DE FLANDRES