The car's origins lie in the DART design by Dizzy Addicott, who sold the project to Jeremy Delmar-Morgan. Delmar-Morgan marketed the result as the Mini Jem. Separately, Jem Marsh of Marcos developed his own version, producing the Mk I Mini Marcos — distinct from the Mini Jem despite the superficial similarity of names. In Sweden, the Mini Marcos was sold through Elmhorn-Troberg Racing Service.
The car used a fibreglass and GRP monocoque body with the Mini's running gear and subframes, giving it a low, aerodynamic form considerably lighter than the standard Mini. Five marks were produced across the car's history. The Mk II introduced sliding windows and a modified front number plate holder. The Mk III added an optional rear hatch. The Mk IV received a standard rear hatch, wind-up windows, and somewhat longer and taller bodywork.
Marcos produced the car from 1965 to 1970. D&H Fibreglass Techniques Limited of Oldham took over production from 1974 to 1981, during which period the Midas succeeded the Mk IV in their lineup. Marcos revived the marque for a third time from 1991 to 1996, producing the Mk V. Following Marcos's final closure, the moulds were acquired by Rory McMath of Marcos Heritage Spares, who relaunched the car as the Heritage Mk. VI and GT, the latter a dedicated racing variant.
The Mini Marcos earned its lasting reputation as the only British car to complete the 1966 24 Hours of Le Mans. Driven by Jean-Louis Marnat and Claude Ballot-Lena, the car finished 15th overall in a field dominated by factory prototype machinery. The Le Mans car was used for several subsequent races before being sold, and was eventually stolen in Paris in October 1975. It remained missing for over four decades until it was found in December 2016. A Marcos works entry at the 1967 24 Hours of Le Mans retired after only 13 laps.
Beyond Le Mans, the Mini Marcos set four British land speed class records — the flying mile, half-mile, half-kilometre, and kilometre — for cars up to 1600 cc.
A small number of Mini Jem and Marcos-derived cars were built in Australia. John Taylor of Taylorspeed in Adelaide introduced the Taylorspeed Jem at a local show in 1968, offered as a kit designed to accept standard Mini running gear. Only ten examples were built across two series: a Mk I with an oval-bottomed rear window and a Mk II with a square rear window. The cars were heavily modified by their individual builders and no two were identical. One example was sold in Singapore.