Tellingly, the film was made during the long interim of the Chinese Civil War when hostilities between Chinese nationalists and the Communists were suspended in order to fight off the Japanese invasion during World War II.
According to Hollywood columnist Erskine Johnson, Joseph Cotten tested for the role of the minister in the film. He also referred to the project as David O. Selznick's version although screen credits list no such connection (Newspaper Enterprise Association, "Erskine Johnson's Hollywood," The Sa Bernardino Daily Sun, San Bernardino California, Sunday 1 February 1942, Volume 48, page 20.)
Vincent Price had to put on weight for the film, to appear fat, because he starved so much for his two previous movies: The Eve of St. Mark (1944) and The Song of Bernadette (1943), to appear slim.
The only Oscar-nominated performance by Gregory Peck in a non-Best Picture nominated film. Peck received his first Academy Award nomination for Best Actor for the film, although he lost to Ray Milland in The Lost Weekend (1945). The Keys of the Kingdom also received Academy Award nominations for Best Art Direction, Best Cinematography (both for black and white) and Best Music (scoring of a dramatic or comedic picture).