Aubry began his military career in 1742, when he was commissioned as a second lieutenant in the Lyonnais Infantry Regiment. After serving in the War of the Austrian Succession as an officer of grenadiers, Aubry left France to take a commission as a captain of colonial troops in Louisiana. During the French and Indian War, he was the commander of the French forces at the Battle of Fort Ligonier. He was later captured and imprisoned by the British after the French defeat at the Battle of La Belle-Famille. After his release, he was made a Chevalier de St. Louis and military commander of Louisiana.