 With the overthrow of the monarchy one year later, (10 August 1792), he was elected to the National Convention (3 September), sat among the "Montagnards", joined the Jacobin Club, and voted in favor of Louis XVI' execution ("sans appel ni sursis" – without appeal or delay) on 17 January 1793.An opponent of the Girondists, Vadier opposed the proscription of Jean-Paul Marat, and following the fall of the Girondists travelled to Ariège to actively oppose the Federalist Revolt there.On 14 September 1793, he was named member of the Committee of General Security, soon becoming its President, where he made his deepest mark on the Revolution.