The Riley 12 was a medium-sized premium priced saloon or drophead coupé (also available as a bare chassis) which was available from mid 1939 though it was not announced by The Motor magazine as a new car until July 1939.

Riley still retained a lot of autonomy after their acquisition by Lord Nuffield and this car was Riley's attempt to keep up with the fashions of the late thirties with helmet-style front mudguards and a bigger boot and slightly heavy styling.

The Adelphi in particular had been very successful for Riley and so it made sense to carry this theme forward with the new model.

With access to the Nuffield parts bin, Riley could adopt the MG/Wolseley synchro gearbox in place of the American Borg Warner overdrive box in place of the Riley sector box.

[citation needed] The steering was by Bishop Cam, the column adjustable for length.