In contemporary wartime San Francisco, chemist and blackmailer Albert Baker (Frank Ferguson) is killed by hit man Philip Raven (Alan Ladd), who recovers a stolen chemical formula. Raven is double-crossed by his employer, Willard Gates (Laird Cregar), who pays him with marked bills and reports them to the Los Angeles Police Department as stolen from his company, Nitro Chemical Corporation of Los Angeles. Raven learns of the set up and decides to get revenge. LAPD detective lieutenant Michael Crane (Robert Preston), who is vacationing in San Francisco to visit his girlfriend, nightclub singer Ellen Graham (Veronica Lake), is immediately assigned the case. He goes after Raven, but the assassin eludes him.
Meanwhile, Gates hires Ellen to work in his LA nightclub. She is taken to a clandestine meeting with Senator Burnett (Roger Imhof), where she learns that Gates and Nitro Chemical are under investigation as suspected traitors, and is recruited to spy on Gates. She and Gates board a train for Los Angeles, followed by Raven. By chance, Raven and Ellen sit next to each other. The next morning, Gates is alarmed when he sees them asleep with Raven's head on her shoulder. He wires ahead to alert the police, but Raven forces Ellen at gunpoint to help him elude them again. He is about to kill her but is interrupted by workmen, allowing Ellen to flee. She tries to contact Crane, but he has left San Francisco to return to LA.
That evening the suspicious Gates invites Ellen to his Hollywood mansion, where his chauffeur Tommy (Marc Lawrence) knocks her unconscious to set up a fake suicide. Crane goes to the mansion looking for Ellen but Gates has already left. While Crane questions Tommy, Raven arrives and hides outside, where he sees Tommy discard Ellen's purse, to keep Crane from spotting it. Raven realizes that Ellen is in danger. After Crane leaves, Raven knocks Tommy down a flight of stairs when the chauffeur denies Ellen is still there. Raven searches the house and rescues her. Tommy recovers and warns Gates at his club, where Crane has caught up with him. Raven and Ellen are confronted as they enter the club, so Raven takes her hostage as he flees. She surreptitiously drops monogrammed playing cards as a trail of "breadcrumbs". The police corner them in a railroad yard but wait for daylight to move in.
Raven reveals to Ellen that he was orphaned at a young age and raised by an abusive aunt. One day, he snapped while she was beating him and killed her, for which he was imprisoned in reform school; there, he was abused by the other children. She tells him that the formula he recovered was for a poison gas that Nitro is selling to the Japanese and begs him to extract a signed confession instead of killing Gates. Ellen helps Raven escape the dragnet, hoping she has appealed to his patriotism. However he breaks his promise to her and kills a policeman to get away.
Raven arrives as Nitro Chemical conducts a gas attack drill and its employees wear gas masks, obscuring their faces. Gates orders Tommy to guard his door. Tommy spots Raven and gives chase, but Raven knocks him out. Raven disguises himself in Tommy's uniform and gas mask to surprise Gates, forcing him to take him to company president Alvin Brewster (Tully Marshall), the mastermind of the treasonous Nitro sale. Raven barricades himself with them when the police and Ellen arrive, and coerces both into signing a confession. Brewster dies of a heart attack while trying to kill Raven, who then kills Gates. Crane is lowered on a scaffold and exchanges gunfire with Raven, wounding him. Raven passes up the opportunity to kill Crane when he sees Ellen helping the detective. Other police fatally shoot Raven, but he lives long enough to assure Ellen that he got the confession and receive her assurance that she did not turn him in.
Graham Greene's novel This Gun for Hire was published in the U.S. in 1936, and several movie studios considered obtaining rights to the book. These included 20th Century Fox and Paramount Pictures. Paramount bought the rights in 1936, and announced Gertrude Michael as a possible star. Later that year the cast was announced as being Akim Tamiroff, Ray Milland and Ida Lupino with Dore Schary writing the script.
However, the film would not be made for several more years. It was reactivated in 1941 with Frank Tuttle attached as director. Veronica Lake was announced early as a female lead with Macdonald Carey, who had been signed by Paramount following his appearance on Broadway in Lady in the Dark — mooted as a possible male lead. Tuttle had some difficulty casting the part of Raven. He later claimed that he looked at six stars but none were suitable. (One of them was Alan Baxter.) Alan Ladd screen tested. By September, Ladd had been cast and signed to a long term Paramount contract.
Robert Preston was given the other main role — replacing Carey. Lake and Preston were given above-the-title star billing, with Ladd given an "and introducing" credit. However, it was clear during filming that Ladd would be the breakout star. Shortly afterwards, The New York Times reported that:
Tuttle and the studio are showing more than a passing enthusiasm for Ladd. He has been trying to get a foothold in pictures for eight years but received no encouragement although he tried every angle known to town - extra work, bit parts, stock contracts, dramatic schools, assault of the casting offices. Sue Carol, the former silent star who is now an agent, undertook to advance the youth's career two years ago and only recently could she locate an attentive ear. Then the breaks began.
Before This Gun for Hire was even completed, Paramount announced that their next film for Ladd would launch him as a star. It was to be a version of The Glass Key (also 1942).
Although Ladd only received fourth billing, the film made him a star, due to fan reaction and critical praise.
Bosley Crowther, film critic for The New York Times, wrote a rave review:
One shudders to think of the career which Paramount must have in mind for Alan Ladd, a new actor, after witnessing the young gentleman's debut as a leading player in that studio's This Gun for Hire... Obviously, they have tagged him to be the toughest monkey loose on the screen. For not since Jimmy Cagney massaged Mae Clarke's face with a grapefruit has a grim desperado gunned his way into cinema ranks with such violence as does Mr. Ladd in this fast and exciting melodrama. Keep your eye peeled for this Ladd fellow; he's a pretty-boy killer who likes his work... Mr. Ladd is the buster; he is really an actor to watch. After this stinging performance, he has something to live up to—or live down.
Crowther characterized the film itself as a "fast and exciting melodrama."
The Los Angeles Times wrote that "to say the film is a success is an understatement."
According to Ladd's biographer, the film ended up making $12 million. However Variety puts the films rentals for 1942 at $1 million.
This Gun For Hire was adapted as a radio play on the July 3, 1942, broadcast of Philip Morris Playhouse with Marlene Dietrich starring, on the January 25, 1943 broadcast of Lux Radio Theater and the April 2, 1945 broadcast of The Screen Guild Theater. Alan Ladd reprised his role in both adaptations while Veronica Lake reprised in the latter, but was replaced with Joan Blondell in the former.
Paramount Pictures later adapted the story as Short Cut to Hell (1957), directed by James Cagney, his only directorial effort.