Dommartin received his first commission in 1785, serving as a captain of the artillery. Seriously wounded during the siege of Avignon, he was unable to take up his appointment as artillery commander at the Siege of Toulon in 1793. Therefore, an ambitious young artillery captain named Napoleon Bonaparte assumed command of the French artillery, with notable success. Dommartin then served in the Army of Italy. During the Montenotte Campaign, he led a brigade in the Second Battle of Dego and in the Battle of Mondovì. Later, he commanded the artillery at the Battle of Rovereto.