An experienced soldier, he took part in the Aragonese Crusade in 1284 and defeated the Flemings in 1297 at the Battle of Furnes. He was again sent into Flanders in July 1302, where he began to ravage the countryside and attempted to take the town of Kortrijk. He then met the Flemish army at the Battle of the Golden Spurs. His infantry advanced with great success against the Flemings (mostly city militia), but he ordered their recall to allow his cavalry to make the final, victorious charge. But on the broken, marshy ground, his knights were unable to gain enough momentum to break the Flemish shieldwall, and they were knocked down and slaughtered. Robert led some of the reserves in a second charge in an attempt to reverse their fortunes, but was cut down by the Flemish infantry.
After his death, his daughter Mahaut inherited Artois, but his grandson Robert unsuccessfully tried to claim it.