The story of the rise of politician Willie Stark from a rural county seat to the governor's mansion is depicted in the film. He goes into politics, railing against the corruptly run county government, but loses his race for county treasurer, in the face of unfair obstacles placed by the local machine. Stark teaches himself law, and as a lawyer, continues to fight the local establishment, championing the local people and gaining popularity. He eventually rises to become a candidate for governor, narrowly losing his first race, then winning on his second attempt. Along the way he loses his innocence and becomes as corrupt as the politicians he once fought against. As he rises, Stark philanders and gets involved with many women, taking his PR man/journalist Jack Burden's own girlfriend, Anne Stanton, as his mistress.
Stark's son Tommy drinks to deal with his feelings about his father, eventually crashes his car, injuring himself and killing his female passenger. When Stark bullies Tommy into playing a football game, Tommy becomes paralyzed after a brutal hit.
Stark, who had always dealt with those who got in his way by any means, begins to see his world start to unravel and he discovers that not everyone can be bought off.
The story has a complex series of relationships. All is seen through the eyes of the journalist, Jack Burden, who admires Stark and even when disillusioned still sticks by him. Stark's campaign assistant, Sadie is clearly in love with Stark and wants him to leave his wife, Lucy. When Stark's reputation is brought into disrepute by Judge Stanton (Anne's uncle), he seeks to blacken the judge's name. When Jack finds evidence of the judge's possible wrongdoing, a quarter century earlier, he hides it from Stark. Anne gives the evidence to Stark, who uses it against her uncle, who immediately commits suicide. Anne seems to forgive Stark, but her brother, Adam, the surgeon who helped save Tommy's life after the car crash, cannot. After Stark wins an impeachment investigation, Adam assassinates Stark. The doctor in turn is shot down by Sugar Boy, Stark's fawning assistant. Having lost their respect for him, Jack and Anne agree to find a way to destroy Stark's reputation just as he dies.
Broderick Crawford as Willie Stark
John Ireland as Jack Burden
Joanne Dru as Anne Stanton
John Derek as Tom Stark
Mercedes McCambridge as Sadie Burke
Shepperd Strudwick as Adam Stanton
Ralph Dumke as Tiny Duffy
Anne Seymour as Mrs. Lucy Stark
Katharine Warren as Mrs. Burden
Raymond Greenleaf as Judge Monte Stanton
Walter Burke as Sugar Boy
Will Wright as Dolph Pillsbury
Grandon Rhodes as Floyd McEvoy
Larry Steers as Man at Impeachment Hearing (uncredited)
Houseley Stevenson as Madison the newspaper editor
Paul Ford as State Senator and impeachment prosecutor
based on the 1946 Robert Penn Warren novel of the same name