Prince Ilia, known in Russia as the "tsarevich" Ilya Georgyevich, was commissioned in March 1812 as a podporuchik of the Jäger Guards Regiment, with which he served in the war with Napoleon's Grande Armée. Under the command of Major-General Karl von Bistram, he fought at Smolensk and was marked for distinction at Borodino. In September 1812 illness forced him to retire from active service to Moscow. During the 1813–14 campaign he served in the Reserve Army of General Dmitry Lobanov-Rostovsky in the vicinity of the besieged French fortress of Modlin in Poland. In 1823 Prince Ilia was transferred to the Izmailov Guards Regiment with the promotion to colonel. He retired with that rank the same year.