Vito Marcantonio was the most consequential radical politician in the United States in the twentieth century. Elected to Congress from New York's ethnically Italian and Puerto Rican East Harlem slums, Marcantonio, in his time, held office longer than any other third-party radical, serving seven terms from 1934 to 1950. Colorful and controversial, Marcantonio captured national prominence as a powerful orator and brilliant parliamentarian. Often allied with the U.S. Communist Party (CP), he was an advocate of civil rights, civil liberties, labor unions, and Puerto Rican independence. He supported social security and unemployment legislation for what later was called a "living wage" standard. And he annually introduced anti-lynching and anti-poll tax bills a decade before it became respectable. He also opposed the House Un-American Activities Committee, redbaiting, and antisemitism, and fought for the rights of the foreign born. He was a bold outspoken opponent of U.S. imperialismThis article can also be found at the Monthly Review website, where most recent articles are published in full.Click here to purchase a PDF version of this article at the Monthly Review website.