A prologue establishes the journalistic bona fides of 60 Minutes producer Lowell Bergman (Pacino) and host Mike Wallace (Plummer) as they prepare to interview Sheikh Fadlallah for 60 Minutes. Later, Bergman approaches Jeffrey Wigand (Crowe)—a former executive at the Brown & Williamson tobacco company—for help translating technical documents. Wigand agrees, but intrigues Bergman when he refuses to discuss anything else, citing a confidentiality agreement. B&W later coerce Wigand into a more restrictive agreement, leading Wigand to accuse Bergman of betraying him. Bergman subsequently visits Wigand to defend himself and investigate the potential story. Wigand, though apparently possessing very damaging information, is hesitant to jeopardize his severance package with B&W by revealing anything.
Wigand’s family move into a more modest house, and Wigand begins working as a teacher. One night Wigand finds evidence of trespass, and receives a sinister phone call. Meanwhile, Bergman contacts Richard Scruggs, an attorney representing Mississippi in a lawsuit against the tobacco industry, suggesting that if they deposed Wigand, it could negate his confidentiality agreement and give CBS cover to broadcast the information; Scruggs expresses interest. Some time later, Wigand receives an emailed death threat and finds a bullet in his mailbox. He contacts the FBI, but the agents who visit him are hostile and confiscate his computer. A furious Wigand demands that Bergman arrange an interview, in which Wigand states that he was fired after he objected to B&W intentionally making their cigarettes more addictive.
Bergman later arranges a security detail for Wigand’s home, and the Wigands suffer marital stress. Wigand testifies in Mississippi, over the objections of B&W attorneys, despite having been served with a gag order. On returning home, he discovers that his wife Liane (Diane Venora) has left him and taken their daughters. Eric Kluster, the president of CBS News, decides not to broadcast Wigand’s interview, after CBS legal counsel Helen Caperelli warns that the network is at risk of legal action from B&W. Bergman confronts Kluster, believing that he is protecting the impending sale of CBS to Westinghouse, which would enrich both Kluster and Caperelli. Wallace, and their executive producer Don Hewitt, both side with Kluster. Wigand is appalled, and terminates contact with Bergman.
Investigators probe Wigand’s personal history and publish their findings in a 500-page dossier. Bergman learns that The Wall Street Journal intends to use it in a piece questioning Wigand’s credibility. He convinces the editor of the Journal to delay while Jack Palladino, an attorney and investigator, evaluates it. After infighting at CBS over the Wigand segment, Bergman is ordered to take a “vacation”, as the abridged 60 Minutes segment airs. Bergman contacts Wigand, who is both dejected and furious, accusing Bergman of manipulating him. Bergman defends himself and praises Wigand and his testimony. Scruggs urges Bergman to air the full segment to draw public support for their lawsuit, itself under threat by a lawsuit from Mississippi’s governor. Bergman is unable to assist, and privately questions his own motives in pursuing the story.
Bergman contacts an editor at The New York Times, disclosing the full story and events at CBS. The Times prints the story on the front page, and condemns CBS in a scathing editorial. The Journal dismisses the dossier as character assassination and prints Wigand’s deposition. Hewitt accuses Bergman of betraying CBS, but finds that Wallace now agrees that bowing to corporate pressure was a mistake. 60 Minutes finally airs the original segment, including the full interview with Wigand. Bergman tells Wallace that he has resigned, believing 60 Minutes’s credibility and integrity is now permanently tarnished.