Famous for his speeches at the Jacobin club, he was elected a member of the municipality of Paris, then of the Legislative Assembly, and later of the National Convention.
He presented a famous report in the Constituent Assembly on the organization of the army, but is better known by his eloquent speech on the 28th of February 1791, at the Jacobin Club, against Mirabeau, whose relations with the court were beginning to be suspected, and who was a personal enemy of Lameth.
This expriest, this disillusioned Jacobin and skilful spinner of cobweb constitutions, enjoyed for a time the chief reputation in France.
His oracular reserve, personal honesty and consistency of aim had gained him the suffrages of all who hoped to save France from the harpies of the Directory and the violent rhetoricians of the now reconstituted Jacobin Club.
The Jacobin Club was closed, thanks to the ability of Fouche, the new minister of Police; but the hopes of Sieyes were dashed by the death of General Joubert, commander of the Army of Italy, at the disastrous battle of Novi (15th of August).