He presented a famous report in the Constituent Assembly on the organization of the army, but is better known by his eloquent speech on 28 February 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.

During the next months, as leaders of the Feuillant club, they established their belief that the flight of the King to Varennes was all because of the faulty revolutionary process that prohibited any manner of compromise.

[8] He served in the army as maréchal-de-camp under Nicolas Luckner and the Marquis de la Fayette, but was accused of treason on 12 August 1792 for protesting against the Attack on the Tuileries.

[12] He wrote various novels and articles, his two most prominent being: Histoire de l'Assemblée constituante and Mémoires publiés avec introduction et notes par Eugène Welvert.

[13] In Histoire de l'Assemblée constituante, he introduced this work by displaying how he did not wish to write a book of biased anecdotes, nor provide a side of the revolution that states he was a main player, even though he was in a position to recall the most prominent events.