The film's opening intertitle reads:
"This story is told against a background of political unrest in a city of Northern Ireland. It is not concerned with the struggle between the law and an illegal organisation, but only with the conflict in the hearts of the people when they become unexpectedly involved."
The city and the organisation are never explicitly named, but the protagonist, Johnny McQueen (James Mason), is the IRA-like group's leader in the city. Johnny has been hiding the past six months since his escape from prison in a house occupied by Kathleen Sullivan (Kathleen Ryan) - who loves him - and her grannie.
Johnny has been ordered to rob a mill to obtain funds. His men, however, are a bit uneasy about his fitness for the task, having noticed a change in him since his escape; he has expressed his new belief that negotiation might achieve their goals more effectively than violence. Dennis (Robert Beatty) offers to take his place, but Johnny turns him down.
Johnny, Nolan (Dan O'Herlihy) and Murphy get the money. As they leave, Johnny is confronted by an armed cashier. Johnny is shot in the left arm before he kills the cashier. Pat (Cyril Cusack) drives off at high speed before Johnny is fully inside the getaway car. Johnny falls off. While his confederates argue about what to do, Johnny gets up and dashes away.
Dennis orders the others to report to headquarters. Along the way, however, the trio arouse the suspicion of the police, out in force on a manhunt for the robbers. They are pursued, but get away. Pat and Nolan stop off at Theresa O'Brien's place; Murphy does not trust her and goes elsewhere. She betrays the pair to the authorities. As they leave, they are gunned down after they start shooting.
Dennis finds Johnny, but the police show up nearby. Dennis is captured after drawing them away.
Johnny makes his way toward Kathleen's place, but collapses in the street. Passersby Maureen and Maudie take him home, thinking he has been struck by a passing lorry. When they discover who he is, Johnny departs and gets into a parked hansom cab. "Gin" Jimmy (Joseph Tomelty), the cabdriver, comes out and starts looking for a fare, unaware he already has a wanted man for a passenger. When he finds out, he drops Johnny off as quickly as he can.
Shell (F. J. McCormick) spots him dumping the now nearly unconscious fugitive. A poor man, he goes to Catholic priest Father Tom (W. G. Fay), hoping for a financial reward. By chance, Kathleen arrives shortly afterward, looking for help. Father Tom persuades Shell to fetch Johnny. Shell, while dropping off his pet bird at home, has to fend off another resident, (the possibly mentally unstable) painter Lukey (Robert Newton), who wants him to pose some more for him. Meanwhile, Johnny revives and stumbles into a private booth in a crowded bar. Proprietor Fencie (William Hartnell) recognises him; wanting no trouble, he closes his establishment a bit early. He then recruits Shell and the persistent Lukey, who have separately converged on the bar, to take Johnny away in a cab. Over Shell's protests, Lukey takes Johnny back to his studio to paint his portrait. Failed medical student Tober (Elwyn Brook-Jones) tends to Johnny's wound as best he can. Johnny hallucinates, thinking Father Tom is talking to him. Johnny then speaks aloud (drooling crazily throughout) parts of 1 Corinthians 13, first verse 13 ("When I was a child ..."), then 1-2 ("Though I speak ... and have not charity, I am nothing.").
When a sympathetic police inspector (Denis O'Dea), who had earlier led a search of Katleen's home and warned her against getting involved, shows up to try to get information from Father Tom, Kathleen slips away. She arranges passage on a ship for Johnny and goes searching for him. Shell starts Johnny toward Father Tom's, then goes ahead and encounters Kathleen. She takes Johnny to the ship, but finds the police closing in. Johnny is too far gone to see them. When he asks, "Is it far?", Kathleen replies, "It's a long way, Johnny, but I'm coming with you." She then draws a gun and starts firing, forcing the policemen to shoot back, killing them both.James Mason as Johnny McQueen
Robert Newton as Lukey
Cyril Cusack as Pat
F. J. McCormick as Shell
William Hartnell as Fencie
Fay Compton as Rosie
Denis O'Dea as Inspector
W. G. Fay as Father Tom
Maureen Delaney as Theresa O’Brien
Elwyn Brook-Jones as Tober
Robert Beatty as Dennis
Dan O'Herlihy as Nolan
Kitty Kirwan as Grannie
Beryl Measor as Maudie
Roy Irving as Murphy
Joseph Tomelty as ‘Gin’ Jimmy, the cabbie
Aside from Mason, the supporting cast was drawn largely from Dublin's Abbey Theatre. Among the other members of the Organisation are Cyril Cusack, Robert Beatty, and Dan O'Herlihy. On his travels, Johnny meets an opportunistic bird-fancier played by F. J. McCormick, a drunken artist played by Robert Newton, a barman (William Hartnell) and a failed surgeon (Elwyn Brook-Jones). Denis O'Dea is the Inspector on Johnny's trail, and Kathleen Ryan, in her first feature film, plays the woman who loves Johnny. Also of note are W. G. Fay—a founder of the Abbey Theatre—as the kindly Father Tom, Fay Compton, Joseph Tomelty, and Eddie Byrne. Albert Sharpe plays a bus conductor. A number of non-speaking parts were filled by actors who later went on to achieve a modicum of fame, including Dora Bryan, Geoffrey Keen, Noel Purcell, Guy Rolfe and Wilfrid Brambell (a standing passenger in the tram scene). Few of the main actors in the film actually manage an authentic Ulster accent.
The cinematographer was Robert Krasker, in his first film for director Reed, lighting sets designed by Ralph Brinton and Roger Furse.
The bar set was based on the Crown Bar in Belfast; contrary to some sources, it was a studio set built at D&P Studios in Denham, Buckinghamshire, and was not filmed in the real Crown. However, much of the film was shot on location: exterior scenes were shot in West Belfast, although some were shot at Broadway Market, Hackney in London.
Composer William Alwyn was involved writing the leitmotif-based score from the very beginning of the production. It was performed by the London Symphony Orchestra conducted by Muir Mathieson.
The film's violent ending attracted advance criticism from the censors, and had to be toned down in the finished film.
It was the eighth most popular film at the British box office in 1947.
The film received the BAFTA Award for Best British Film in 1948. It was nominated for the Golden Lion award at the Venice Film Festival in 1947, and nominated for a Best Film Editing Oscar in 1948.
Filmmaker Roman Polanski has repeatedly cited Odd Man Out as his favourite film. Polanski feels that Odd Man Out is superior to The Third Man, generally considered to be Reed's masterpiece:
I still consider it as one of the best movies I've ever seen and a film which made me want to pursue this career more than anything else... I always dreamt of doing things of this sort or that style. To a certain extent I must say that I somehow perpetuate the ideas of that movie in what I do.
Odd Man Out was presented on Suspense February 11, 1952. James Mason and his wife, Pamela Mason, starred in the 30-minute adaptation.