For two years he attended a school for young workers, and in early 1940 graduated from the Shostka chemical technical school. Kozhedub learned to fly aircraft in the Shostkinsk aeroclub and joined the Soviet army in 1940. He graduated from the Chuguev Military Air School in 1941 at the start of the German invasion of the Soviet Union, but he was retained as an instructor. Kozhedub remained at the school for two years where he trained many young Soviet pilots.
In 1949 Kozhedub graduated from the Air Force Academy.
After his first military flight on 26 March 1943, Ivan Nikitich operated on the Voronezh Front and, in July over the Kursk battlefields. His first kill was a Junkers Ju 87 Stuka shot down during the Battle of Kursk on 6 July 1943. By 16 August he had claimed eight air victories. He was promoted to Mladshii Leitenant (Junior Lieutenant). Then his unit moved towards Kharkiv. At this time he usually flew escort for Petlyakov Pe-2 twin-engine bombers. During World War II, he then served as a fighter pilot in several areas (Steppe Front, 2nd Ukrainian Front, 1st Belorussian Front) and at different ranks, starting from senior airman up to the deputy commander of the air regiment. He claimed his 61st and 62nd victories – his final claims – over Berlin on 16 April 1945.
Kozhedub holds the record for the highest number of confirmed air combat victories of any Soviet or Allied pilot (effectively the Allied "Ace of Aces") during World War II. He is regarded as the best Soviet flying ace of the war, and is associated with flying the Lavochkin La-7. He was also reputed to have a natural gift for deflection shooting, i.e. aiming ahead of a moving target at the time of firing so that the projectile and target will collide.
Kozhedub's World War II record consists of: 330 combat missions, 120 aerial engagements, 62 enemy aircraft shot down, including one Me 262 jet fighter (possibly Uffz Kurt Lange of 1KG(J)54.)
In April 1951, promoted to Polkovnik (colonel), he commanded the 324th IAD (Fighter Air Division) and dispatched to Antung airfield on the China-North Korea border to fly the MiG 15 during the Korean War supporting the North Korean forces. He was not given permission to participate in combat missions. Under his leadership the 324th IAD claimed 239 victories, including 12 Boeing B-29 Superfortresses for the loss of 27 MiG-15s in combat and 9 pilots.
In 1956 he graduated from the High Command Academy, after which he was promoted to General. From 1971 he served in the Central Office of the Soviet Air Force and from 1978 in the general inspection group of the Ministry of Defense of the USSR. He was made an Aviation Marshal in 1985.