He fought at the Battle of Leipzig and the Battle of Borodino. In March 1814, Alexander I was concerned for the safety of his brothers Nicholas and Constantine, who were involved in the occupation of Paris. He dispatched Kleinmichel to warn them and advise them to return to Basel. After succeeding in this, Kleinmichel was made Aide-de-Camp to the Tsar. The event also brought him to the attention of the future Tsar Nicholas I