Tom Tryon was nominated for a Golden Globe in 1963 for his performance, but suffered immensely under Otto Preminger's notorious abusive treatment of actors. At one point during filming, Preminger fired Tryon in front of his parents when they visited the set, then rehired him after being satisfied that Tryon had been sufficiently humiliated. This type of treatment was a big turning point for Tryon, who eventually retired from acting and turned to a successful writing career.
The movie includes one real-life character and incident. In 1938, Bishop Fermoyle is sent to Vienna to deal with Cardinal Theodor Innitzer (played by Josef Meinrad), the real-life Archbishop of Vienna. Innitzer's public support for the "Anschluss" annexation of Austria by Nazi Germany put him at odds with the Vatican, who ordered him to retract his statement of support. In the months following the annex, the Nazis reneged on their earlier agreements with the Church of Vienna, and prohibited Church institutions and Catholic newspapers. Afterwards, Innitzer became a critic of the Nazi regime. In October, 1938 (as seen in the film), Innitzer held a Catholic rally in Vienna, in which he proclaimed, "There is just one Führer: Jesus Christ." The following day (also seen in the film), a Nazi mob stormed Innitzer's Vienna offices and ransacked the Archbishop's residence.
Cameraman Leon Shamroy felt that Bradford Dillman would have been better casting for the title role. However, he appreciated the professionalism of director Otto Preminger, who completed this very large-scale picture in just 53 days - quite a change from Shamroy's immediately previous assignment on "Cleopatra", which occupied him for over a year.