He was not employed for some years, but in 1804, when the war party in the Austrian court needed a general to oppose the peace policy of the Archduke Charles, Mack was made quartermaster-general of the army, with instructions to prepare for a war with France.
Han gik i nogle år uden arbejde, men i 1804 da krigspartiet ved det østrigske hof skulle bruge en general til at opponere mod ærkehertug Karls fredspolitik, blev Mack Generalquartiermeister over hæren, med ordre til at forberede en krig mod Frankrig.