In July 1791, after the flight of Louis XVI, the constitutional king, Rewbell left the Jacobin Club and joined the "Feuillants". During the session of the Legislative Assembly, after the Constituent Assembly was dissolved in September of that year, he exercised the functions of "procureur syndic", and was subsequently secretary-general of the "département" of Haut-Rhin. He was elected to the Republic's National Convention in 1792, and was its envoy to the Rhineland, advocating the union of the Electorate of the Palatinate and other territories with France. A zealous promoter of the Trial of Louis XVI, he was absent on mission at the time of the king's condemnation.