Korchagin volunteered for the Imperial Russian Army during World War I, during which he was wounded multiple times and decorated. He rose from private to junior officer and joined the Red Army during the Russian Civil War. After serving with the Internal Troops in the latter, Korchagin was stationed in Soviet Central Asia during the 1920s, serving in various command and staff positions. In the mid-1930s he became commander of a mechanized brigade before being arrested during the Great Purge. Korchagin was released in 1940 and reinstated in the Red Army, commanding the 17th Tank Division at the outbreak of Operation Barbarossa. Korchagin led the division in the Battle of Smolensk and continued in command after it was reorganized into a brigade due to heavy losses. After his brigade was destroyed in the Battle of Moscow, Korchagin became responsible for aerosani units before commanding the 17th and 18th Tank Corps in the Battle of Voronezh. He became commander of the 2nd Mechanized Corps, which later became the 7th Guards Mechanized Corps, in September 1942, leading it for the rest of the war. Made a Hero of the Soviet Union for his leadership of the corps during the Battle of the Dnieper, Korchagin held army command postwar.