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 IHe was responsible for building the Saint Petersburg–Moscow Railway and for restoring the Winter Palace after the 1837 fire.
It was rumored that Nicholas I promoted his career because Kleinmichel adopted the Emperor's illegitimate children as his own.
His first wife divorced him, citing his sexual dysfunction.