Keir joined the Russian and Austrian armies in Italy early in 1799, and served in the campaigns of 1799, 1800 and 1801. He was present at the battles of Novi, Rivoli, Mondovi, and Sanliano. He also served in the gunboats at the Siege of Genoa (1800) and in several actions in the mountains of Genoa, when the Austrians and Russians lost nearly thirty-three thousand men. He was also at the Battle of Marengo and the sieges of Alessandria, Sanaval, Tortona, Cunio and Savona.