In 1752, his cousin, the Fürst Franz Joseph, died childless; his own father had died in 1749, as had his uncle. The allodial seat came to him. After his succession, he gave up state bureaucratic service and joined the Army. He was assigned to the Regiment "Colledo" in 1754, and in the following year, promoted to Colonel and regimental commander. He led this regiment during the Battle of Lobositz, the first battle of the Seven Years' War and the following year he was promoted to Major General, on 25 June 1757 (effective 26 January 1757).