The XK120 was launched in open two-seater or roadster form at the 1948 London Motor Show as a test-bed and show car for the new Jaguar XK engine designed by Jaguar Chief Engineer William Heynes.

Beginning in 1948, the first 242 cars wore wood-framed open 2-seater bodies with aluminium panels. Production switched to the 1cwt or 112 lb (51 kg) heavier all-steel in early 1950.The "120" in the name referred to the aluminium car's 120 mph (193 km/h) top speed (faster with the windscreen removed), which made it the world's fastest production car at the time of its launch. In 1949 the first production car, chassis number 670003, was delivered to Clark Gable.1951 XK120 Fixed Head CoupeThe XK120 was ultimately available in three versions or body styles, first as an open 2-seater described in the US market as a roadster (OTS) then as a fixed head coupé (FHC) from 1951 and finally as a drophead coupé (DHC) from 1953, all two-seaters and available with Left (LHD) or Right Hand Drive (RHD). However, certain Special Equipment roadster and fixed head coupe cars were produced between 1948 and 1949 denoted by an 'S' preceding the chassis number. XK120s were also highly successful in racing and rallying.Total production of the Jaguar XK120 FHC was 294 right hand drive and 1471 Left Hand Drive.