Arguably the finest Western second-generation MBT, the Chieftain served in the British Army for over three decades and remains in service with numerous foreign users to this day. The Chieftain, along with the US M60, was built with strong armor protection from the start, in contrast to the preference for mobility in its NATO contemporaries the Leopard 1 and AMX-30. As such, it featured a combination of rolled and cast steel armor in the turret, with more advanced Stillbrew appliqué armor used in later British Army variants. The Chieftain's protection was further enhanced thanks to its steeply sloped hull and turret design, the latter which did not incorporate a mantlet in order to provide greater gun depression. As far as firepower, it featured a more powerful punch than any other NATO tank thanks to its fully stabilized Royal Ordnance L11 120-mm rifled gun, the same gun fitted on its eventual successor, the Challenger 1. Other features include NBC protection and advanced fire control systems for its day. Perhaps its only drawback, however, was relatively poor cross-country performance due to an underpowered multi-fuel engine (which was later improved) as well as a coil spring suspension. Despite its unmatched performance, the Chieftain did not see any NATO orders, and was exported only to various Middle Eastern countries including Iraq, Iran, Jordan, Kuwait, and Oman. It saw extensive action during the Iran-Iraq war, with mixed success against Soviet-designed Iraqi tanks. Kuwaiti Chieftains also saw action against Iraqi T-72s during the 1990 invasion of Kuwait.

The first prototypes of the FV4202 were built in 1956, and were later refined into the FV4201 prototypes built in 1960-61. This was then introduced as the Chieftain Mk. 1 for training, and later the Mk. 2 for actual service in 1967, both of which were fitted with 650 hp engines. Equipment upgrades resulted in the Mk. 3, which was followed by the final production variant, the Mk. 5 with an uprated engine among other improvements including increased ammunition-carrying capacity. Other incremental upgrades resulted in the Mk. 6, Mk. 7, and Mk. 8, before being retrofitted with an integrated IFCS (Improved Fire-Control System) developed by GEC-Marconi in the Mk. 9 and Mk. 10. The last two marks, Mk. 11, and Mk. 12, added Stillbrew appliqué armor, a Thermal Observation and Gunnery System (TOGS), and a new NBC system to existing vehicles. Other variants included the Chieftain AVRE (Armoured Vehicle Royal Engineers), Chieftain ARV (Armoured Recovery Vehicle), Chieftain AVLB (Armoured Vehicle-Launched Bridge), and Chieftain ARRV (Armoured Repair and Recovery Vehicle).