Initially he was incorporated into the Austrian army. On 10 December 1806, he moved to the newly formed Polish Army in the cavalry of Colonel Wojciech Męciński. This unit was transformed into the 4th Military Regiment of the Duchy of Warsaw. Franciszek Fornalski participated in campaigns in Prussia (1806), Galicia (1809), Russia (1812) and Saxony (1813). He participated in battles under the Wały, Friedland, Żarnów, Smolensk, Mozhaysk, Borodino, Vyazma, Cherykaw, Berezina, Wittenberg and Leipzig (" Battle of the Nations"). After Napoleonic Wars we was working as a forest guard in the Kunów area till his retirement (3 November 1847).