Along with Styles, 22, English actors Jack Lowden and Aneurin Barnard are in talks to join the production, said The Hollywood Reporter.
The cast also includes this year's Oscar winner Mark Rylance, Tom Hardy and Sir Kenneth Branagh.
Production on the drama is set to begin in May, which will be shot on 65mm large format film and Imax.
The movie centers on the British military evacuation of the French city of Dunkirk in 1940, one of the biggest battles during the way.