The Audax body was designed by the Rootes Group helped by the Raymond Loewy design organisation, who were involved in the design of Studebaker coupés in 1953, with the Studebaker design cues prominent on all Rootes mid-sized saloon cars up to the introduction of the Arrow series in the late 60s. Announced in May 1956 the car went through a succession of annual facelifts with each given a series number finishing with the Series VI in 1965. The Vanguards model below is the Series IIIA from 1959. Over the years the engine was increased in capacity from 1390 cc to 1725 cc in the Series VI. There were Singer Gazelle and Sunbeam Rapier variants of all these Hillman Minx models and the names were reused on derivatives in the later Rootes Arrow range. Some models were re-badged in certain markets, with the Sunbeam and Humber marques used for some exports.

A Series III de Luxe saloon with 1494 cc engine tested by the British magazine The Motor in 1958 had a top speed of 76.9 mph and could accelerate from 0–60 mph in 25.4 seconds. A fuel consumption of 31.8 miles per imperial gallon was recorded. The test car cost £794 including taxes of £265.