Impoverished, angry, and poorly educated, Bigger Thomas drifts around the seedy South Side of Chicago until he finds work chauffeuring a wealthy, liberal white family named the Daltons. On his first evening of work, Bigger drives the Daltons' college-age daughter Mary and her Communist boyfriend Jan Erlone around town while the two of them get drunk. Bigger carries the intoxicated Mary to her bedroom and becomes sexually aroused while putting her to bed; when Mrs. Dalton, who is blind, comes to the door, Bigger silences Mary by covering her face with a pillow and inadvertently smothers her to death. He burns her corpse in the furnace and desperately tries to destroy evidence of the crime and frame Erlone for it, but when a reporter discovers Mary's bones in the furnace, the police quickly close in on Bigger and take him to jail. 

The final section of the book recounts Bigger's trial. His lawyer, a Jewish-American Communist named Boris Max, pleads that Bigger is not responsible for his violent actions because social forces drove him to crime, and he urges the judge to spare Bigger the death penalty. The state's prosecutor responds that Bigger is a cold-hearted, depraved criminal and must die as the law requires. The judge rules for the prosecution and sentences Bigger to death. In the final scene, Max attempts to console Bigger, but Bigger rebuffs him. "What I killed for, I am!" Bigger insists, and Max leaves him to his fate.