Unusually for a Colonial officer Dumas' military career started in the Agenois Regiment and fought in the War of Austrian Succession and came to Canada in 1750 with the rank of captain. Became known as a skilful negotiator with Indians. Sent to Fort Duquesne. Took command of the French forces at Monongahela when Beaujeu was killed and recieved the Order of St Louis at the age of 35. Became favoured by Vaudreuil and acted as adjutant for the campaign against Fort William Henry 'because of his diligence, our troops, and even our Canadians, yielded nothing to the troupes de terre [French regulars] in the most precise execution of [their] military duties.'
Commanded a brigade during the defence of Quebec and the battle of Sainte-Foy. More here.