The German advance led to a friction within the British government, between those who were willing to make peace treaty with Hitler, and Churchill, who refused.
The film also stars Kristin Scott Thomas, Lily James, Ben Mendelson, and Stephen Dillane.
At the 2017 Oscars, the film earned six nominations, including Best Picture.
Oldman, who went through a complete physical transformation, was responsible for the film winning the Best Makeup and Hairstyling Oscar.
Released by Focus Features, The Darkest Hour world premiered at the Telluride Film Fest on Sep. 1, then played at Toronto Fest. It opened in limited release on November 22, at the height of the awards season, and received wide distribution December 22, after receiving Golden Globes and Critics Choice nominations.