Burt Lancaster was the original choice to play Sam Flusky in Under Capricorn, but the part went to Joseph Cotteninstead because Lancaster was deemed too expensive.
Margaret Leighton appeared with her future husband Michael Wilding in this film. After their marriage in 1964, they worked together several more times, but, by his own admission, Wilding preferred retirement and was happy just to be a supportive audience member for his wife. In this film, Michael Wilding played Charles Adare and Margaret Leighton played Milly.
According to Michael Wilding's autobiography "The Wilding Way", on one occasion while Ingrid Bergman and Michael Wilding were in the middle of a passionate love scene Hitchcock let out a howl of pain, then in the most gentle tone said "Please move the camera a little to the right. You have just run over my foot." The X-ray revealed later that the camera's weight had broken Hitchcock's big toe.
According to the Book "Its only a Movie", Alfred Hitchcock originally wanted Arthur Laurents to do the screenplay. After reading Helen Simpson's novel "Under Capricorn", Arthur Laurents told Hitchcock that he was the wrong writer for the project. So Alfred Hitchcock hired James Bridie to do the screenplay instead.
Hitchcock began to use the "Ten Minute Take" of continuous one-reel shooting which he had enjoyed refining on his previous film Rope, but as the process proved far more difficult here than in the enclosed apartment-set drama, only a couple of sequences were ultimately shot for the finished print.
In 1958, Cahiers du Cinema (French Film Magazine) voted Under Capricorn as one of the ten greatest films of all time.
In his autobiography "Vanity Will Get You Somewhere", actor Joseph Cotten referred to this film as "Under Corny Crap". Supposedly he had also done so on set, invoking Hitchcock's ire; intentionally or otherwise, the director did not use him again for six years.
Many French critics consider Under Capricorn as one of Hitchcock's finest films.
Alfred Hitchcock:
about five minutes into the movie in the town square wearing a coat and a brown hat. Ten minutes later he is one of three men on the steps of government house.