Chrysler, who were owners of the brand Plymouth wanted to counter the growing popularity of several upcoming foreign brands that were more smaller and agile, unlike their American counterparts that were huge sized and petrol guzzlers.

This prompted the then Chrysler President Tex Colbert to institute a technical committee to come up with something new to counter car imports. He involved world-famous designer Virgil Exner to design something smaller in size and yet offer maximum space for passengers with luggage included.

The project that started in 1957 was so much secretive that only the factory General Manager and 180 engineers working on the project knew about the secret car. It was labelled Project A901. Fellow employees thought that Chrysler was involved in making a secret vehicle for the government as the building where they were designing was kept out of bounds. Chrysler's management wanted to create a hype, deliberately.

After making 20 prototypes using 50 different types of engines, what turned out was a super successful car.

IBM computers were used for testing noise, vibration and even suspension. What was beneath the hood was also an innovation. The engine had a cylinder block that was given a 30° inclination so that the overall height of the engine was reduced and at the same time allowed the model to have a lower engine hood. This innovative design also allowed the car maker to have the intake and exhaust manifolds with long runners. The design was called a Slant-6 engine.

The Plymouth Valiant debuted at the Auto Show in London in 1959 with a strong tagline that said – Nobody's kid brother, this one stands on its own four tires. It was available to the public for sale in 1960. The Valiant was supposed to be the quietest car ever made.

In few years the Valiant turned out to be one of the best-exported models for the Chrysler company with sales as far as Finland, South Africa, Sweden and Australia (abroad they were sold as Chrysler Valiant). 

Valiant’s were assembled by Chrysler between 1963-1976 with little changes. A 2-door hardtop variant was named Acapulco, after a Mexican seaside city.