"Theater Guild on the Air" broadcast a 60 minute radio adaptation of the movie on January 7, 1951 with Joseph Cotten reprising his film role.
Graham Greene based the character of Harry Lime on British double agent Kim Philby, who was Greene's superior in the British Secret Intelligence Service.
Carol Reed had three separate film units working most days of production: a daytime unit, a nighttime unit and a sewer unit. Reed insisted upon directing each unit, resulting in him working 20 hour days.
Bernard Lee was second choice for Sgt. Paine. The actor who was first choice was not hired because of billing issues.
David O. Selznick insisted the filmmakers use Alida Valli for the female lead. Actually, Carol Reed and Alexander Korda were happy with the choice. Selznick became dissatisfied that Reed had Valli wear more plain clothes, wanting her to look glamorous and beautiful throughout. Reed won out on this aspect, due to the support of Korda.
David O. Selznick was resistant to Carol Reed's idea of casting Orson Welles as Harry Lime, since Selznick had labeled Welles as "box office poison".
Orson Welles evaded production assistants and assistant director Guy Hamilton while traveling in Europe when he was supposed to be on location filming in Vienna. During Welles' unexpected absence, Carol Reed had to film around him, getting numerous spectacular shots in the sewers seen in the finished film. Numerous body doubles for Welles were used, included Hamilton, who was made to wear an over-sized hat and padded coat to approximate Welles' larger size. Reed himself doubled for Welles' hands when they reach through the sewer grade. When Welles finally arrived, he was 2 weeks late.
Orson Welles said that when he agreed to play Harry Lime, he was offered either a straight salary or a percentage of the profits. Welles chose the salary but he later regretted it because the film went on to become such a huge hit, the percentage was ultimately worth far more than the salary.
Orson Welles starred in a radio series ("The Lives of Harry Lime," 1951-52) based on the early adventures of his character in this film.
Cary Grant was considered for the part of Harry Lime. Conicidentally, Grant was a regular lunchtime visitor to the set of the film when the shooting returned to London sound-stages.
Joseph Cotten re-created his role in the Lux Radio production of "The Third Man" with Evelyn Keyes playing Alida Valli's role. Orson Welles was not in this radio play.
Although David O. Selznick theoretically produced, the rest of the crew hated him and his ideas (he suggested once to Graham Greene that the film be called "Night Time in Vienna").
Director Carol Reed originally wanted James Stewart for the role of Holly Martins; producer David O. Selznick insisted on Joseph Cotten, who was under contract to Selznick's production company at that time.
During meetings between Graham Greene and Carol Reed with David O. Selznick, Greene was less than impressed with Selznick, who had (according to Selznick's own son) "become something of a parody of himself". Greene later mocked Selznick's dependency at the stage on the drug Dexedrine, better known as "speed". Coincidentally, Reed also became hooked on Dexedrine while shooting the time-consuming film. Both Reed and Selznick were operating on as little as 2 hours of sleep a day.
Film debut of Robert Brown.
Harry Lime's character name may be derived from Graham Greene's own name. Henry=Harry Graham Greene (Green)= Lime. Others say he chose the surname because it "reminded him of the quicklime where murderers were buried."
In one shot in the Wienkanal, a security officer passes by a wall with the engraving "O5," which was the secret symbol of the Austrian resistance against Nazi occupation. ("O5" represents "OE" or "Ö," the first letter of "Österreich," the native name for Austria.)
Once he finally arrived in Vienna, Orson Welles refused to film various scenes in the sewers. Due to his protests, various sets replicating the Vienna sewers had to be constructed by Alexander Korda on sound-stages back in England.
Ranked #5 on the American Film Institute's list of the 10 greatest films in the genre "Mystery" in June 2008.
Rumors have long since been widespread that Orson Welles wrote all of Harry Lime's dialogue and even that he took over the direction of his own scenes. Everyone involved, including Welles himself, have always insisted that the film was directed by only Carol Reed. Welles did claim that he wrote most of Lime's dialogue, which is also a fabrication. The extent of Welles' contributions were Lime's grumbling about his stomach problems (which were improvisations) and the famous "cuckoo clock" spiel at the end of the ferris wheel scene.