The XK120 was Jaguar's first totally new car since the end of World War II. Jaguar's founder, William Lyons, designed the car in three months in 1948 and his factory built a prototype for the Earls Court Motor Show in just two weeks. Demand for the car was so great and immediate that all the 1949 and 1950 models were made out of aluminum while the factory prepared the tooling to build the cars out of steel.

The car was fitted with a new six-cylinder, twin-overhead camshaft engine of 3442cc that could produce 160 horsepower and a sustained speed of 120 miles per hour, providing the 120 its name. Its revolutionary design featured independent front suspension and hydraulic breaks, which unfortunately had a tendency to wear out quickly. At 5 feet, 1.5 inches, the car was wider than other European sports cars, which allowed roomier leather seats as well as storage in the doors concealed with leather flaps. The car's undercarriage was based on the MK-V Saloon chassis but shortened 18 inches to 14 feet, 6 inches. Famous owners included Clark Gable, Phil Hill and Sterling Moss.