Based on the A10 Cruiser tank, the Valentine was privately designed by Vickers-Armstrongs (hence its lack of a General Staff "A" designation) and was submitted to the War Office on 10 February 1938. The development team tried to combine the weight of a cruiser tank (so that suspension and transmission parts of the A10 could be used) with the greater armour of an infantry tank, which resulted in a very small vehicle with a cramped interior and two-man turret. Though its armour was still weaker than the Infantry Tank II Matilda and, due to a weaker engine, it shared the same top speed, the new design was easier to produce and much less expensive.

The War Office was initially deterred by the size of the turret and the crew compartment. Concerned by the situation in Europe, however, it finally approved the design in April, 1939. The vehicle reached trials in May, 1940, which coincided with the loss of nearly all of Britain's equipment during the evacuation at Dunkirk. The trials were successful and the vehicle was rushed into production as Infantry Tank III Valentine. The Valentine remained in production until April 1944, becoming Britain's most produced tank during the war with 6,855 units manufactured in the UK (by Vickers, Metropolitan-Cammell Carriage and Wagon and Birmingham Railway Carriage and Wagon), and a further 1,420 in Canada. They were the Commonwealth's main export to the Soviet Union under the Lend-lease Act, with 2,394 of the British models being sent and 1,388 of the Canadian Pacific built models, and the remaining 30 being kept for training.