Having chosen a military career, Poniatowski joined the Austrian imperial army, where he was commissioned lieutenant in 1780, in 1786/1788 promoted to colonel, and, when Austria declared war against Ottoman Empire in 1788, he became an aide-de-camp to Emperor Joseph II. Poniatowski fought in that war and distinguished himself at the storming of Šabac on 25 April 1788, where he was seriously wounded. At Šabac he also reportedly saved the life of a younger colleague, Prince Karl Philipp Schwarzenberg. Later their military paths crossed repeatedly, as friends and foes, and at the end of Poniatowski's career Schwarzenberg delivered the crushing blow at the Battle of Leipzig in which Poniatowski was killed.