In the United Kingdom the Mark I was produced between 1959 and 1967 at the Longbridge Plant near BMC's headquarters, with production in Australia continuing until 1970.

The production model differed from the original prototype (affectionately named "The Orange Box" because of its colour) due to the addition of a modified front subframe, on which the engine was mounted, and by the engine being mounted with the carburettor at the back, rather than at the front, as in the prototype, to reduce wear on the gearbox.

Issigonis' suspension featured the use of rubber cones as springs: the spring rate of rubber changes with compression, allowing the suspension to adapt to passenger load variations (a full passenger load could actually double the tiny vehicle's gross weight).

This unique design was adapted from Issigonis's home-built racer and built for the Mini by Alex Moulton.

The tiny 10-inch (250 mm) wheels helped to reduce the intrusion of wheel arches into the interior of the vehicle and allowed a modest amount of additional luggage space in a "boot" area behind the rear seats.

1,000 of this iteration were commissioned by management, intended for and designed to meet the homologation rules of Group 2 rally racing.

By the time production of the Cooper model ended in 1967, 12,274 of these popular cars had been sold to the public.

The 1,275 cc (1.3 L; 77.8 cu in) engined models continued through the Mk2 Mini, finally being killed off in 1971 in the Mk3 bodyshell.

The new model featured redesigned doors with conventional interior handles and wind up windows (with quarter vents), hydrolastic suspension, key operated starter, a remote gearshift mechanism (like the Cooper) and the engine was upgraded to the 998 cc version.

The K received the more powerful 1098 cc engine (from the Morris 1100) as well as 4-speed synchromesh transmission and upgraded instruments.

Chassis numbers for production changes are given in italics, where necessary in the format Austin/Morris Certain components fitted to Mark I cars were stamped with the date on which they were made.