Charles-Grégoire was born and baptised at Cherbonnières, roughly 19 km (13 miles) to the east of Saint-Jean-d'Angély, between Poitiers and Bordeaux in rural western France. He was a younger son of Henri-Charles de Beauchamps (1701-1777), lord of the manor at Cherbonnières. His mother, Madeleine-Dorothée de Lescours, was probably also of aristocratic provenance. He embarked on his military career late in 1757 when he took part in the disastrous (for France) Battle of Rossbach, receiving but surviving fourteen injuries, and retaining his "colours", albeit in a badly shredded condition. He was awarded the Cross of St Louis for his valour and progressed with a military career that took him, eventually, to the rank of a Maréchal de camp.