Born in Paris, he was in the retinue of the comte d'Artois (future King Charles X), and became an officer in a cuirassier regiment. He served in the American War of Independence, was deputy to the Estates-General of 1789, which subsequently became the National Assembly and National Constituent Assembly. As the Assembly began to divide into factions, Lameth, a constitutional monarchist, was identified with the Feuillants. Since the French Revolution moved toward a Republic, he emigrated.