The working title of this picture was The Phantom Crown. A pre-production news item in HR notes that the picture was titled Maximilian and Carlotta until the suspension of Bette Davis caused the studio to decide to change its production plans from a co-starring vehicle to a vehicle for Paul Muni. The title was then switched to Juarez to reflect the change in focus. Davis eventually was re-written into the story. The CBCS for the film indicates that Charles Middleton was originally set to play the role of Carbajal. A production still for the film illustrates that actress Gail Page tested for the role of "Carlotta." According to the Var review, the picture was shot on Eastman's new high speed film. The film originally ran fifteen reels, and Warner Bros. considered cutting it into two pictures. The Mexico City scenes were filmed in Calabasas, CA.
       Warner Bros. files at the USC Library add the following information about the production: the studio had commissioned an original script, hoping that they would not have to purchase the Franz Werfel play to make the film. However, the studio lawyer advised producer Henry Blanke that the similarities between the script and the play were so strong that the legal department felt the studio would be subject to an infringement action. After much analysis, the studio purchased the rights to the play. The picture represented Warner Bros. most ambitious project to date. According to the production files, every detail was exhaustively researched for historical accuracy. The files contained long lists of reference books in both English and Spanish. Press releases refer to the film's extensive research. According to modern sources, the writers had a bibliography of 372 volumes, documents and period photographs. Art director Anton Grot drew 3,643 sketches from which engineers prepared 7,360 blueprints for the exteriors and interiors of the settings. A complete Mexican village was built on the Warner Ranch in Calabasas, CA.
       News items in HR add that to promote the film in South and Central American countries, Warner Bros. arranged a radio broadcast in which representatives from Mexico, Chile, Costa Rica, Brazil and the Pan American Union discussed the picture. Warner Bros. also held a special showing for the president of Mexico.
       Materials in the Warner Bros. Files note that shortly before work began on this film, a Mexican producer named Miguel C. Torres began shooting a film entitled Maximilian and Carlotta starring Conrad Nagel. Warner Bros. advised Torres that they owned all motion picture and collateral rights to the Werfel play and asked him to refrain from using the title Juarez and Maximilian. Lacking money to finish his picture, Torres approached Harry Cohn about distributing the film. To end the threat of another company distributing Torres' film before they could release Juarez, Warner Bros. picked up the film and retitled it The Mad Empress (see below). Brian Aherne was nominated for an Academy Award in the Best Actor in a Supporting Role category.