Marlon Brando was considered for the role of Pierre, but he did not want to work with Audrey Hepburn.
Audrey Hepburn recommended her Roman Holiday co-star Gregory Peck for the role of Pierre, but Henry Fonda was cast instead.
Audrey Hepburn's salary of $350,000 for the film was the highest salary an actress had ever received to date. When notified of her record salary Hepburn modestly told her agent, "I'm not worth it. It's impossible. Please don't tell anyone."
Jeremy Brett was chosen to play Nicholas in part because it was felt he resembled his on-screen sibling, Audrey Hepburn.
Henry Fonda later admitted he had known from the beginning that he was too old for his character, and had only made the film for the money.
For the filming of the epic battle scenes, the producers hired 65 physicians, dressed them as soldiers and scattered them throughout the location to take care of any extras or stuntmen who might get injured during filming of the scenes.
In the Italian post-synchronized version of the film, the following dubbers lent their voice to the English-speaking cast: Maria Pia Di Meo (Audrey Hepburn), Emilio Cigoli (Henry Fonda), Stefano Sibaldi (Mel Ferrer), Arnoldo Foà (Herbert Lom), Mario Besesti (Oskar Homolka), Lidia Simoneschi (Anita Ekberg), Gualtiero De Angelis (Helmut Dantine), Amilcare Pettinelli (Barry Jones), Fiorella Betti (Milly Vitale), Rosetta Calavetta (May Britt) and Carlo Romano (John Mills).Vittorio Gassman dubbed himself.
In the scene where the Rostovs invite Prince Andrei to go hunting with them, Jeremy Brett is the only actor never on a mechanical horse: in all his shots he is clearly on a live horse. Audrey Hepburn, Henry Fonda, Mel Ferrer, Barry Jones and May Britt are all clearly on mechanical horses in their close shots.
King Vidor directed the huge Battle of Borodino sequence himself rather than leave it to a second unit director as was the custom.
The first draft of the screenplay was 506 pages, over 5 times the size of an average screenplay.