Limitations of the existing 2 pounders were apparent even as the gun was first entering service, and an effort was made to replace it with a much more capable weapon starting as early as 1938. The Woolwich Arsenal was entrusted with the development. The 57 mm calibre was chosen for the new gun. Guns of this calibre were employed by the Royal Navy from the late 19th century, and therefore manufacturing equipment was available. The design was complete by 1940, but the carriage design was not completed until 1941. The production was further delayed by the defeat in the Battle of France. The loss of equipment - most of the BEF's heavy equipment had to be left behind in France during Operation Dynamo - and the prospect of a German invasion made re-equipping the army with anti-tank weapons an urgent task, so a decision was made to carry on the production of the 2 pounder, avoiding the period of adaptation to production, and also of re-training and acclimatization with the new weapon. It was estimated that 100 6-pounders would displace the production of 600 2-pounders. This had the effect of delaying production of the 6 pounder until November 1941 and its entry into service until May 1942.
Unlike the 2-pounder, the new gun was mounted on a conventional two-wheeled split trail carriage. The first mass production variant—the Mk II—differed from the pre-production Mk I in having a shorter L/43 barrel, because of shortage of suitable lathes. The subsequent Mk IV was fitted with a L/50 barrel, with muzzle brake. Optional side shields were issued to give the crew better protection, but were apparently rarely used.
The 6 pounder was used where possible to replace the 2-pounder in current British tanks, requiring work on the turrets, pending the introduction of new tanks designed to take the 6-pounder from the outset. The Churchill Marks III and IV, Valentine Mark IX and Crusader Mark III all began to enter service during 1942. The Valentine and Crusader both needed to lose a crew member from the turret. Those tanks designed to take the 6-pounder from the outset were the problematic Cavalier and the Cromwell and Centaur. When the Cromwell went into combat in 1944 it was however armed with the Ordnance QF 75 mm gun, which was a redesign of the 6-pounder to take US 75 mm ammunition and more useful against general targets. The 6-pounder was also fitted to the AEC Armoured Car Mark II.
Although the 6-pounder was kept at least somewhat competitive through the war, the Army nevertheless started development of a more powerful weapon in 1942. Their aim was to produce a gun with the same general dimensions and weight as the 6-pounder, but with improved performance. The first attempt was an 8-pounder of 59 calibre length, but this version proved too heavy to be used in the same role as the 6-pounder. A second attempt was made with a shorter 48 calibre barrel, but this proved to have only marginally better performance than the 6-pounder. The program was eventually cancelled in January 1943.
Instead the 6-pounder was followed into production and service by the next generation British anti-tank gun, the 17 pounder which came into use from February 1943. As a smaller and more manoeuvrable gun, the 6-pounder continued to be used by the British Army not only for the rest of World War II, but also for some 20 years after the war.
A 57/42.6 mm squeeze bore adaptor was developed for the gun but was never adopted.
In addition to the UK, the gun was produced in Canada.
The Combined Ordnance Factories (COFAC) of South Africa produced three hundred examples as well.