The book depicts working-class poverty, the lack of social supports, harsh and unpleasant living and working conditions, and a hopelessness among many workers. These elements are contrasted with the deeply rooted corruption of people in power. A review by the writer Jack London called it "the Uncle Tom's Cabin of wage slavery."
Sinclair was considered a muckraker, or journalist who exposed corruption in government and business. In 1904, Sinclair had spent seven weeks gathering information while working incognito in the meatpacking plants of the Chicago stockyards for the newspaper. He first published the novel in serial form in 1905 in the Socialist newspaper Appeal to Reason and it was published as a book by Doubleday in 1906.
The main character in the book is Jurgis Rudkus, a Lithuanian immigrant trying to make ends meet in Chicago. The book begins with his wife Ona and his wedding feast. He and his family live near the stockyards and meatpacking district, where many immigrants who do not know much English work. He takes a job at Brown's slaughterhouse. Rudkus had thought the US would offer more freedom, but he finds working conditions harsh. He and his young wife struggle to survive. They fall deeply into debt and are prey to con men. Hoping to buy a house, they exhaust their savings on the down payment for a substandard slum house, which they cannot afford. The family is eventually evicted after their money is taken.
Rudkus had expected to support his wife and other relatives, but eventually all—the women, children, and his sick father—seek work to survive. As the novel progresses, the jobs and means the family use to stay alive slowly lead to their physical and moral decay. Accidents at work and other events lead the family closer to catastrophe. Rudkus' father dies as a direct result of the unsafe work conditions in the meatpacking plant. One of the children, Kristoforas, dies from food poisoning. Jonas—the other remaining adult male aside from Rudkus—disappears and is never heard from again. Then an injury results in Rudkus being fired from the meatpacking plant; he later takes a job at Durham's fertilizer plant. The family's hardships accumulate as Ona confesses that her boss, Connor, had raped her, and made her job dependent on her giving him sexual favors. In revenge, Rudkus attacks Connor, resulting in his arrest and imprisonment.
After being released from jail, Rudkus finds that his family has been evicted from their house. He finds them staying in a boarding house, where Ona is in labor with her second child. She dies in childbirth at age 18 from blood loss; the infant also dies. Rudkus had lacked the money for a doctor. Soon after, his first child drowns in a muddy street. Rudkus leaves the city and takes up drinking. His brief sojourn as a hobo in the rural United States shows him that no real escape is available—farmers turn their workers away when the harvest is finished.