The IS-2 tank first saw combat in early 1944. IS-2s were assigned to separate heavy tank regiments, normally of 21 tanks each. These regiments were used to reinforce the most important attack sectors during major offensive operations. Tactically, they were employed as breakthrough tanks. Their role was to support infantry in the assault, using their large guns to destroy bunkers, buildings, dug-in crew-served weapons, and other 'soft' targets. They were also capable of taking on any German AFVs if required. Once a breakthrough was achieved, lighter, more mobile T-34s would take over the exploitation.
The IS-3 first appeared to Western observers at the Allied Victory Parade in Berlin in September 1945. The IS-3 was an impressive development in the eyes of Western military observers, the British in particular, who responded with heavy tank designs of their own.
By the 1950s the emergence of the main battle tank concept—combining medium-tank mobility with the firepower and later armour of the heavy tank—had rendered heavy tanks obsolete in Soviet operational doctrine. In the late 1960s the remaining Soviet heavy tanks were transferred to Red Army reserve service and storage. The IS-2 Model 1944 remained in active service much longer in the armies of Cuba, China and North Korea. A regiment of Chinese IS-2s was available for use in the Korean War, but saw no service there. In response to border disputes between the Soviet Union and China, some Soviet IS-3s were dug in as fixed pillboxes along the Soviet-Chinese border. The IS-3 was used in the 1956 Soviet invasion of Hungary and the Prague Spring in 1968.
During the early 1950s all IS-3s were modernised as IS-3M models. The Egyptian Army acquired about 100 IS-3M tanks in all from the Soviet Union. During the Six Day War, a single regiment of IS-3M tanks was stationed with the Egyptian 7th Infantry Division at Rafah and the 125th Tank Brigade of the 6th Mechanized Division at Kuntilla was also equipped with about 60 IS-3M tanks. Israeli infantry and paratrooper units had considerable difficulty with the IS-3M when it was encountered due to its thick armour, which shrugged off hits from normal infantry anti-tank weapons such as the bazooka. Even the 90 mm AP shell fired by the main gun of the Israeli Defense Force (IDF) M48 Patton tanks could not penetrate the frontal armour of the IS-3s at normal battle ranges. There were a number of engagements between the M48A2 Pattons of the IDF 7th Armoured Brigade and IS-3s supporting Egyptian positions at Rafah in which several M48A2s were knocked out in the fighting. However, in one engagement between a battalion of IS-3s and 90MM-gun-armed M48A3's, 7 IS-3s were destroyed. The slow rate of fire, poor engine performance (the engine was not well suited to hot-climate operations), and rudimentary fire control of the IS-3s proved to be a significant handicap, and about 73 IS-3s were lost in the 1967 war. Most Egyptian IS-3 tanks were withdrawn from service, though at least one regiment of IS-3 tanks was retained in service as late as the 1973 October war. The IDF itself experimented with a few captured IS-3M tanks, but found them ill-suited to fast-moving desert tank warfare; those that were not scrapped were turned into stationary defensive pillbox emplacements in the Jordan River area.
After the Korean War, China attempted to reverse-engineer the IS-2/IS-3 as the Type 122 medium tank. The project was cancelled in favour of the Type 59, a copy of the Soviet T-54A.