Geoffroi was a knight in the service of King Jean II of France and a founding member of the Order of the Star, an order of chivalry founded on 6 November 1351 by Jean II of France similar to the Order of the Garter (1347) by Edward III of England.
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We know from the Chronicles of Froissart that de Charny traveled to Scotland by order of the French King on at least two occasions and was well known to the Scottish nobles of the time.
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Geoffroi took Aimery captive to St. Omer, decapitated him, quartered his body, and displayed it on the town gates.
Some time in 1348, without the knowledge of either King Edward or King Philip, Amery entered into a secret agreement with Sir Geoffrey de Charney, a French knight and governor of nearby Saint-Omer, for the sale of Calais to Sir Geoffrey in exchange for the sum of 20,000 crowns.
In 1355 he served under the Black Prince in Aquitaine, taking part in his march to the Loire and his victory at the Battle of Poitiers, where he was credited by the French historian Jean Froissart with the slaying of the French knight Geoffroi de Charny.