He received Artois as an appanage, in accordance with the will of his father (died 1226) on attaining his majority in 1237 (aged twenty-one). In 1240 Pope Gregory IX, in conflict with the Emperor Frederick II, offered to crown Robert as emperor in opposition to Frederick, but the French count refuse to pretend to such a title.
Robert died while leading a reckless attack on Al Mansurah, without the knowledge of his brother King Louis IX. He and the Templars accompanying the expedition charged into the town and became trapped in the narrow streets. According to Jean de Joinville, he defended himself for some time in a house there, but was at last overpowered and killed. In Egypt it is believed that Sultan Qutuz killed him, although it is more likely that an anonymous soldier did so. According to Matthew Paris who is not considered reliable by modern historians, he fled in disgrace at the height of the battle, and drowned while trying to cross a river named Thanis (a branch of the Nile).