At McClure's magazine, Steffens became part of the celebrated muckraking trio of himself, Ida Tarbell, and Ray Stannard Baker. He specialized in investigating government corruption, and two collections of his articles were published as The Shame of the Cities (1904) and The Struggle for Self-Government (1906). In 1906, he departed McClure's, along with Tarbell and Baker, to form American Magazine.
In 1910 he covered the Mexican Revolution and began to view revolution as preferable to reform. In 1919, he visited the Soviet Union, where he developed a short-lived enthusiasm for communism that had soured by the time he wrote his memoirs, published in 1931. He died in 1936.