Having begun his military career in 1792, he joined the cavalry branch on a permanent basis in 1803 and subsequently saw steady promotion and was given various commands of heavy cavalry units. A part of the Grande Armée in 1805, he took part to the War of the Third Coalition. In 1806, at the outbreak of the War of the Fourth Coalition, Lhéritier was promoted to Colonel and given the command of the 10th Cuirassiers. In this capacity, he was noted for his brave charge at the Battle of Eylau in 1807. Two years later, during the War of the Fifth Coalition, he made an impression on his superiors, especially during the Battle of Aspern-Essling and Battle of Znaim. As a result, he was promoted to Brigadier General and given the command of a cuirassier brigade, before taking part to the French invasion of Russia in 1812. The next year, he was promoted to General of Division and was given various commands during the War of the Sixth Coalition. During the 1815 War of the Seventh Coalition, Baron Lhéritier commanded a mixed dragoon and cuirassier division, at the head of which he charged during the Battle of Waterloo. Lhéritier's active service effectively ended soon after Napoleon I's second abdication, but he did hold two significant military functions during the Second Restoration.