The film was shot in just 35 days, using some of the sets from Quo Vadis (1951), which were dismantled, flown from Rome to Hollywood and then re-assembled for this film. Producer John Houseman confirmed that it was never intended that the film be shot in color, as he and the director Joseph L. Mankiewicz wanted it to have the urgency of a newsreel, not to look like a costume epic.
James Mason and Joseph L. Mankiewicz enjoyed a strong working relationship following 5 Fingers (1952) the year before. Marlon Brando was very conscious of this and saw that Mankiewicz was favoring Mason in many of the key scenes. Brando threatened to walk off the picture unless the balance was restored to his character.
The film's soundtrack was actually recorded in four-track stereo, although it had not been filmed in widescreen, but the movie was eventually released in mono. If it had been released in four-track stereo, this film, and not The Robe (1953), which was made both in CinemaScope (a screen ratio of 2.55:1) and standard "Academy ratio" (1:37:1), would have been the first motion picture released using that method of recording. "Julius Caesar" was eventually released in stereo on laserdisc and DVD.
Marlon Brando became good friends with John Gielgud during filming and frequently consulted Gielgud on how to deliver the verse. Gielgud invited Brando to come to London to do a Shakespeare season on the London stage under his direction, but it never happened.
Producer John Houseman had also produced a version of the play on Broadway in 1937 which had starred Orson Welles to great acclaim. The two had fallen out in the intervening years so Welles was never considered for the film.