At the close of the month he resigned his post on being elected, in spite of his youth, a deputy to the National Convention by the "département" of Seine-et-Oise, and he began his legislative career by defending the conduct of the Commune during the massacres. He took his seat upon The Mountain, and showed himself one of the most vigorous Jacobins, particularly in his defence of Jean-Paul Marat, on 26 February 1793; he voted in favor of the execution of King Louis XVI, and was elected a member of the Committee of General Security on 21 January 1793.