Issigonis' friend John Cooper, owner of the Cooper Car Company and Formula One Manufacturers Champion in 1959 and 1960, saw the potential of the little car, and after some experimentation and testing, the two men collaborated to create a nimble, economical, and inexpensive car. The Austin Mini Cooper and Morris Mini Cooper debuted in September 1961.
The original 848 cc engine from the Morris Mini-Minor was increased to 997 cc, boosting power from 34 bhp (25 kW) to 55 bhp (41 kW). The car featured a tuned engine, double SU carburetors, and 7" disc brakes, a first at the time in a small car. 1,000 of this iteration were commissioned by management, intended for, and designed to meet the homologation rules of, Group 2 rally racing. The 997 engine was replaced by a shorter stroke 998 cc unit in 1964. By the time production of the Cooper model ended in 1967, 12,274 of these popular cars had been sold to the public. A more powerful Mini Cooper, dubbed the "S", was developed in tandem and released in 1963. Featuring a 1071 cc engine and larger disc brakes, 4,030 Cooper S's were produced and sold until the 1071 model was deleted in August, 1964. Cooper also produced two models specifically for circuit racing, rated at 970 cc and a 1275 cc, both of which were also offered to the public. The smaller engine model was not well received and only 961 were built with 970 cc engines until the model was discontinued in April 1965. The 1275cc engined models continued through the Mk2 Mini, finally being killed off in 1971 in the Mk3 bodyshell.