Engelhardt, who was also carried on the roll of the Novotroitskoye Cuirassier Regiment, was often used as a courier of messages between ministers of the Russian Cabinet and their counterparts in Germany and England.
In April 1784, Engelhardt was made Potemkin's adjutant general, and on June 26 of that year was transferred to the Smolensk Dragoon Regiment.
January 20, 1795, by decision of the State Military Board, Engelhardt was dismissed from the service for ill health with the rank of brigadier.
During the 1806 War of the Fourth Coalition against Napoleon, Engelhardt was commander of the Livonia Zemstvo police guarding the border with East Prussia.
During the 1812 campaign, Engelhardt led a force of volunteers and participated in the defense of Riga against the French under Marshal Macdonald; in recognition of his service, he was awarded the Order of St. Anne, second degree with diamonds.