Vaillant entered the French army in 1809 in the corps of engineers. He served in the French invasion of Russia (1812) and the next year became a prisoner of war after the Battle of Kulm. During the Hundred Days Vaillant fought at Ligny and Waterloo. Vaillant commanded a battalion in the 1830 campaign against Algiers. Promoted to lieutenant colonel, he served under Gérard in the expedition into Belgium in 1831.