The Chieftain was an evolutionary development of the successful cruiser line of tanks that had emerged at the end of the Second World War. British engineers had learned during the war that their tanks often lacked sufficient protection and firepower compared to those fielded by the enemy, and that this had led to high casualty levels when faced with the superior German tanks in World War II. The Centurion addressed this to a great degree, combining higher levels of armour and an improved gun, which made it at least equal to any of the contemporary medium tanks. However, the introduction of the Soviet IS-3 heavy tank forced the introduction of their own Conqueror heavy tank, armed with a 120 mm (4.7 in) gun. A single design combining the firepower of the Conqueror's 120 mm gun with the mobility and general usefulness of the Centurion would be ideal.
Leyland, who had been involved in Centurion, had built their own prototypes of a new tank design in 1956, and these led to a War Office specification for a new tank. The General Staff specification drew on experience of Centurion in the Korean War and Conqueror. The tank was expected to be able to engage the enemy at long range and from defensive positions, be proof against medium artillery. To this end, the gun was to have a greater angle of depression than the 8 degrees of Conqueror and better frontal armour. The tank was expected to achieve 10 rounds per minute in the first minute and six per minute for the following four.
The first few prototypes were provided for troop trials from 1959, this identified a number of changes. Changes to address engine vibration and cooling resulted in redesign of the rear hull. This increased the design weight to nearly 50 tons and as such the suspension (which had been designed for 45 tons) was strengthened. Track pads had to be fitted to protect roads from damage and the ground clearance increased. The design was accepted in the early 1960s.
Britain and Israel had collaborated on the development in its latter stages with a view to Israel purchasing and domestically producing the vehicle. Two prototypes were delivered as part of a four year trial. However, it was eventually decided not to sell the marque to the Israelis, which prompted them to follow their own development programme.
In 1957, NATO had specified that its forces should use multi-fuel engines. The early BL Engine delivered around 450 bhp (340 kW) to the sprocket, which meant a top road speed of around 25 mph (40 km/h) and cross country performance was limited. This was further hampered by the Horstmann coil spring suspension, which made it a challenge to drive cross country and provide the crew with a comfortable ride. Due to the cylinder linings being pressure fitted, coolant leaks within the cylinder block were common, resulting in white smoke billowing from the exhaust.
In the late 1970s, engine design changed with the introduction of Belzona which was used to improve the lining seals. Engine output also increased, with later engines delivering some 850 bhp (630 kW) to the sprocket. This meant better performance and an increased speed. However, cross-country performance remained limited.
Several aspects of Chieftain design were trialled by the production of the FV4202 "40-ton Centurion" with a reclined driver position and mantleless gun mounting.