In September 1975, Howard Beale, the longtime anchor for the UBS Evening News, learns from friend and news division president Max Schumacher that he has just two more weeks on the air because of declining ratings. The following night, Beale announces to his audience that he will commit suicide on next Tuesday's newscast. UBS tries to immediately fire Beale, but Schumacher intervenes so that he can have a dignified farewell. Beale promises to apologize for his outburst, but once on the air, he launches into a rant about life being "bullshit". Beale's outburst causes ratings to spike, and much to Schumacher's dismay, UBS executives decide to exploit the situation. When Beale's ratings soon top out, programming chief Diana Christensen reaches out to Schumacher with an offer to help "develop" Beale's show. He declines the professional proposal but accepts her more personal pitch; the two begin an affair.
When Schumacher decides to end Beale's "angry man" format, Christensen persuades her boss, Frank Hackett, to slot the evening news show under the entertainment division so she can develop it. Hackett bullies UBS executives to consent and fire Schumacher. In one impassioned diatribe, Beale galvanizes the nation, persuading viewers to shout, "I'm as mad as hell, and I'm not going to take this anymore!" from their windows. He is soon hosting a new program called The Howard Beale Show, top-billed as "the mad prophet of the airwaves". The show becomes the most highly rated program on television, and Beale finds new celebrity preaching his angry populist message in front of a live studio audience that, on cue, chants his signature catchphrase: "We're as mad as hell, and we're not going to take this anymore!" Schumacher and Christensen's romance withers as the show flourishes, but in the flush of high ratings, the two ultimately find their way back together; Schumacher separates from his wife of over 25 years for Christensen.
Seeking another hit, Christensen cuts a deal with a terrorist group called the Ecumenical Liberation Army (ELA) for a new docudrama series, The Mao Tse-Tung Hour, for which the ELA will provide exclusive footage of their activities. Meanwhile, Beale discovers that Communications Corporation of America (CCA), the parent company of UBS, will be bought out by a larger Saudi conglomerate. He urges his audience to pressure the White House to quash the deal. This panics UBS because the network's debt load has made the merger essential for its survival. CCA chairman Arthur Jensen arranges a meeting with Beale, describing the interrelatedness of the participants in the international economy and the illusory nature of nationality distinctions. Jensen scolds Beale and persuades him to abandon his message and preach his new "evangel".
Christensen's fanatical devotion to her job and emotional emptiness ultimately drive Schumacher away, warning her that she will self-destruct if she continues on her current path. Audiences find Beale's new sermons on the dehumanization of society depressing and ratings start to slip, yet Jensen refuses to fire him. Seeing its two-for-the-price-of-one value – solving the Beale problem while at the same time sparking a boost in season-opener ratings – Christensen, Hackett and the other executives decide to hire the ELA to assassinate Beale on the air. The assassination succeeds, putting an end to The Howard Beale Show and kicking off the second season of The Mao Tse-Tung Hour. A voice-over proclaims, "This was the story of Howard Beale: the first known instance of a man who was killed because he had lousy ratings."
