During the French Revolution, he was one of the commanders of the Republican army, especially during the Siege of Mainz (1792) and he distinguished himself in Cassel (Mainz). In 1793, shortly after the military reorganization, he was a lieutenant colonel of the 93rd Regiment, formerly the Duke of Enghien's regiment; the first battalion of this regiment served in the Army of the Rhine under Adam Philippe, Comte de Custine; the second at Strasbourg, and the grenadiers at Mainz. Although only a brigadier general, he commanded the Army of the Rhine from 14 February to 29 April 1795. He had not sought command of the Army of the Rhine—indeed, Desaix, and others had flat out refused to take command and had finally convinced the Committee in Paris that Schaal was the man for the job, despite his being a brigadier and they, generals of division—but Schaal had taken the command against his better judgement and executed it as best he could. To give the others credit, they had followed his orders precisely, as uninspired as they were.