Kleist served in the Napoleonic Wars and fought at Jena. In 1807 he went on extended leave but by 1808 he was put in command of an infantry brigade and the next year he was made commandant of Berlin. During the War of Liberation he was given a corps with which he fought in the battles of Kulm and Leipzig. In 1814, he was given the title Count of Nollendorf (from the German name of the town Nakléřov, now part of Petrovice in the Czech Republic) for his decisive role in this battle.