Baldwin V had fought a war with his uncle Count Henry IV of Luxembourg to establish Namur as independent from Luxembourg in 1190 and in 1194, Emperor Henry VI declared Namur to be a margraviate. Baldwin's will left Namur to Philip, but as a fief of Hainault.[1] However, Count Theobald I of Bar, who had married Henry of Luxembourg's daughter, Ermesinda, refused to relinquish Namur and attacked Philip, besieging him in Namur.[2] The war lasted for three years until the Treaty of Dinant, signed on 26 July 1199, recognised Philip as holder of Namur.[2]
Following Baldwin's capture at Adrianople, Philip was summoned to a meeting by King Philip Augustus of France at Pont de l'Arche.[4] Philip was forced to swear fealty to the king of France and give Baldwin's daughters as wards of the King.[5][4] Along with these exactions Philip was forced to marry Marie, daughter of Philip Augustus and Agnes of Merania.[4]
In Namur, Philip reigned as a peaceful and pious promoter of social development. He intervened as the mediator between many feuding lords. He died of dysentery on 9 October 1212, in Valenciennes. He had designated his twin sister Yolande as heir.