Following  the success of the Javelin in various competitions including Le Mans 24 hour, it was decided decided to use its power train in a sports car for export in the hope of increasing their inadequate steel allocation.

The complete Jowett Jupiter was displayed for the first time in New York in April 1950 prior to this the chassis had been displayed at the London Motor Show of 1949.

 Eberan von Eberhorst, formerly with Auto Union, designed and developed the Jupiter's tubular steel chassis. The suspension used soft torsion bars and anti-roll bars front and rear with independent suspension at the front. The engine was mounted very far forward ahead of the front axle line with the radiator low behind it over the gearbox. Reg Korner of Jowett put a steel framed aluminium drophead coupé body with a bench seat for three people. There was no external access to the boot (trunk) and the bonnet (hood) was rear hinged and opened complete with the wings.

These cars were only for export. The plan was for coachbuilders to build bodies and supply the local market.

An initial 75 chassis were supplied to external coachbuilders such as Stabilimenti Farina, Ghia Suisse, Abbott of Farnham and others in Britain. These bodies where expensive considering The Jupiter was only a 1500 c.c. car and so Jowett built their own complete cars The Jowett factory made 731 Mk1 and 94 Mk1a cars. The Mk 1a came out in late 1952 with a little more power (63 bhp) and an opening lid to a boot of larger capacity.

The flat four overhead valve engine of 1486 cc was more highly tuned than in the Javelin and had its compression ratio raised from 7.2:1 to 8.0:1 developing 60 bhp (45 kW) at 4500 rpm giving the car a maximum speed of 85 mph (137 km/h) and a 0-50 mph time of 11.7 seconds. Two Zenith carburettors were fitted to the engine and  a four speed gearbox with column change was used.

Production ceased in 1954

1950 - class win at the  Le Mans 24 Hour race

1951 - class one-two in the  Monte Carlo International Rally

1951 - outright win Lisbon International Rally

1952 – class win at Le Mans 24 hour race