In 1812, by the Tsar's decree, Prince Constantine was enlisted in the Life Guard Cossack Regiment as a "Rittmeister" and promoted to being a "Flügeladjutant" to Tsar Alexander I. He was transferred to the Life Guard Hussar Regiment in 1813. He took part in the war against Napoleonic France from 1812 to 1814. In 1817, Constantine became major-general and appointed as a commander of the 1st Brigade of the 1st Hussar Division. He was awarded the Russian orders of St. Vladimir, 4th Class, St. Anna, 1st Class, and of St. George, 4th Class. Prince Constantine retired from the military service in 1838. He died in Moscow in 1844 and was buried at the Donskoy Monastery.