He was born in Paris. Having served in the American War of Independence under Rochambeau, he was sent in 1789 as deputy to the States-General by the nobles of the bailliage of Péronne. In the Constituent Assembly he formed with Barnave and Adrien Duport a "Triumvirate," which controlled a group of about forty deputies forming the advanced left of the Assembly. He presented a famous report in the Constituent Assembly on the organization of the army, but is better known by his eloquent speech on February 28, 1791, at the Jacobin Club, against Honoré Mirabeau, whose relations with the court were beginning to be suspected, and who was a personal enemy of Lameth. However, after the flight of Louis XVI to Varennes, Lameth became reconciled with the court. He served in the army as maréchal-de-camp under Nicolas Luckner and the Marquis de la Fayette, but was accused of treason on August 15 1792, fled the country, and was imprisoned by the Austrians.
After his release he went into business at Hamburg with his brother Charles and the duc d'Aiguillon, and did not return to France until the Consulate. Under the Empire he was made prefect successively in several departments, and in 1810 was created a baron. In 1814 he attached himself to the Bourbons, and under the Restoration was appointed prefect of Somme, deputy for Seine-Inférieure and finally deputy for Seine-et-Oise, in which capacity he was a leader of the Liberal opposition. He was the author of an important History of the Constituent Assembly (Paris, 2 vols., 1828-1829).
He had two brothers, Théodore Lameth (1756-1854) who served in the American war, sat in the Legislative Assembly as deputy from the department of Jura, and became maréchal-de-camp; and Charles Malo François Lameth.