The film opens at the offices of The Morning Post, where Walter Burns is a high-powered editor. His ex-wife, Hildy Johnson, has returned to the paper to tell him that she is remarrying and moving to Albany with her new husband, the affable but milquetoast Bruce Baldwin. Hildy used to be a reporter at the paper—perhaps its best—but Walter's marital neglect and the unconventional lifestyle of a "newspaperman" proved to be too much for her, and she wants to settle down in a stable life of domestic bliss. When Walter hears the news of Hildy's imminent marriage, he sets to work immediately trying to thwart it. Knowing that there is a high profile execution coming up the following day, Walter convinces Hildy to stay and cover it for the paper by offering to buy a life insurance policy from Bruce, Hildy's finance.
Hildy agrees to cover the case of Earl Williams, the man who shot a police officer and is set to be hanged. Even though Earl is evidently insane (and thus innocent of his crime), the police officer he killed was black, and the corrupt mayor is likely to use Earl's crime (and subsequent execution) to cynically garner the black vote in an upcoming election. The mayor is refusing to sign a reprieve to release Earl on the grounds of insanity, and Walter and Hildy set to work attempting to expose Earl's insanity and the corruption of the mayor. Hildy heads to the pressroom at the criminal courts, but not before getting Bruce to hand over their savings—$500—for fear that Walter will try and swindle Bruce out of it somehow.
At the pressroom, Hildy learns that a psychologist is visiting Earl Williams that day to assess his sanity, and manages to get an interview with Earl before the assessment by bribing the warden. In their interview, Hildy gets Earl to tell her that after he was fired from his job, he spent a lot of time in the park listening to zealots talk about the notion of "production for use," the philosophy that everything should be put to use. He shot the police officer, he tells her, because he had a gun in his hand and he wanted to put it to use. As she leaves, Hildy notices a picture of Mollie Malloy, a woman who took pity on Earl days before his crime.
Hildy returns to the pressroom, where she finds that Mollie Malloy confronting a group of male journalists about their inaccurate and disrespectful depiction of her in the press. Hildy gets a call from Bruce—he has been arrested for stealing a watch. When she hears more, Hildy realizes that Walter had Bruce framed by a gangster associate of his named Louie. She goes and bails Bruce out of jail and brings him back to the pressroom. Leaving Bruce in a cab, Hildy goes up to the pressroom to announce her official retirement, when suddenly gunshots are fired outside. Earl Williams has escaped from jail by pilfering the sheriff's gun while being examined by the psychologist. Suddenly eager to get the scoop, Hildy forgets all about Bruce, calls Walter, and chases the warden down to get the full story.
As the other reporters speculate about how Earl Williams could have escaped from custody, Hildy returns to the pressroom with the actual news of Earl's escape. The easily-bought sheriff comes in and scolds the journalist and Hildy calls Walter to discreetly give him the story, which she bought from the warden for $450 of the 500 that Bruce had given her. She asks Walter to have someone deliver the $450 to her immediately, and Walter sends Louie to deliver her counterfeit money. He also sends a seductive looking woman to visit Bruce in his cab near the pressroom. Soon after Hildy hangs up with Walter, Bruce calls—he's been arrested, this time for interacting with the woman that Walter sent. She promises to bail him out but needs to wait for the money.
The mayor comes into the pressroom and announces that they've located Earl Williams at his home and are going to shoot him. A messenger from the governor's office enters with a reprieve for Earl, and the mayor tries to bribe him into forgetting about the reprieve altogether. The messenger doesn't take the bait, so the mayor ushers him out of the office and delivers the message that whoever kills Earl first will receive $500. Louie comes into the pressroom and gives Hildy the counterfeit $450.
When everyone has left the pressroom, Earl Williams climbs through the window, agitated and holding a gun. He threatens Hildy at first, but she eventually manages to disarm him and calm him down. She calls Walter and tells him that she has Earl, when suddenly Mollie knocks on the door. Hildy lets Mollie in and soon after there is another knock on the door; the other reporters want to come back in and are confused why the door is locked. Fearing that they will steal her story, Hildy gets Earl to climb inside one of the roll-top desks to hide. The journalists come in and wonder if Earl is in the building and grow suspicious of Hildy's secretive behavior. Mrs. Baldwin, Bruce's mother, comes in and demands to know what's going on. Mollie grows more and more upset by the conflict, eventually jumping out the window to the pressroom. The journalists all scramble downstairs to check on her and catch the story of the fall, which gets them off Earl's trail.
Walter comes to the pressroom and Hildy quietly tells him about Earl's hiding spot. Mrs. Baldwin, who is still there, wants to know what's in the desk. When Mrs. Baldwin is startled to see that Earl is hiding in the desk, Walter orders Louie to take her away. Louie slings her over his shoulder and carries her out of the pressroom. As Hildy begins writing a draft of the story, Walter calls Duffy and instructs him to take out the whole front page for the story. Bruce comes in and begs Hildy to come with him, but she is absorbed with her article and doesn't pay much attention to what he is saying. She gives him the counterfeit money and he leaves, telling her that he is leaving on the 9 o'clock train to Albany.
When Hildy finishes writing she realizes that Bruce left and isn't coming back and becomes angry with Walter, who lied that he was. Louie comes back, badly beaten up, and tells them that he doesn't know what happened to Mrs. Baldwin. Shocked, Hildy fears that Mrs. Baldwin was killed and begins frantically calling the hospital. The crowd of journalists and the sheriff return and jostle Hildy to get more information about Earl, when Earl's gun falls out of Hildy's clothes. The sheriff is furious with Hildy and Walter. Mrs. Baldwin comes back to the pressroom and accuses Walter of having her kidnapped and tells the men that Earl is hiding on the desk. When Walter denies her accusations, he accidentally taps the desk in which Earl is hiding, which Earl mistakes for a signal to tap back, revealing his hiding spot.
The mayor comes into the pressroom and orders the sheriff to arrest Hildy and Walter. Just when it looks like the ex-spouses have lost their big story and are going to jail, however, the messenger from earlier comes back with the reprieve, and reveals to the reporters that the mayor bribed him. The mayor has them released, trying to save face, and leaves quickly. When they are left alone, Walter tells Hildy to return to Bruce, that he can never give her what Bruce can. Suddenly the phone rings; it's Bruce, who has been arrested—yet again—for being in possession of counterfeit money. After she hangs up, Hildy breaks down sobbing and admits that for a minute she believed Walter when he said he wanted her to return to Bruce. The couple reunites and plans to get remarried and honeymoon at Niagara Falls. When Walter gets a call from Duffy that there is a strike in Albany, however, the honeymoon quickly turns into a work trip, and the couple leaves for Albany to get the next big story.