While his main goal in describing the working conditions in the meat industry was based on an investigation he conducted for a socialist newspaper with the goal of advancing socialism in the United States, most readers were more concerned with several of the passages exposing health violations and unsanitary practices in the American meat packing industry during the early 20th century. It greatly contributed to a public outcry, which led to reforms including the Meat Inspection Act. Sinclair famously said of the public reaction, "I aimed at the public's heart, and by accident I hit it in the stomach."

The book depicts working-class poverty amid a lack of social support, harsh and unpleasant living and working conditions, and a sense of hopelessness among the many workers. These elements contrasted greatly with the deeply rooted corruption of the people in power. A review by writer Jack London called it the "Uncle Tom's Cabin of wage slavery."

Sinclair had spent seven weeks working incognito in the meatpacking plants of the Chicago stockyards while gathering information for the socialist newspaper, Appeal to Reason. As a journalist who exposed corruption in government and business, he was considered a "muckraker." He first published The Jungle in serial form in the newspaper in 1905 and it was then published as a book in 1906.