In 1741, after service in the imperial army, Carolath-Beuthen entered Prussian service. He was a lieutenant colonel in a life carabiner regiment. In 1743, he was colonel and commander of the Curassier regiment Nr. 8. He served most notably at the Battle of Hohenfriedberg. In the same year, Frederick awarded him the Order Pour le Mérite. In 1751 he received his own cuirassier regiment, No. 9., and began the Seven Years' War as a lieutenant general.