James Patrick Cannon (February 11, 1890 – August 21, 1974) was an American Trotskyist and a leader of the Socialist Workers Party.

Born on February 11, 1890, in Rosedale, Kansas, the son of Irish immigrants with strong socialist convictions, he joined the Socialist Party of America (SPA) in 1908 and the Industrial Workers of the World (IWW) in 1911. He was personally trained by "Big Bill" Haywood, a top IWW leader, and was an IWW organizer throughout the Midwest from 1912-14.

Following his expulsion from the Communist Party USA in 1928, of which he had been a founding member and the National Chairman of its legal entity,[2] the Workers Party of America, Cannon was national secretary of the Communist League of America, Workers Party of the United States and Socialist Workers Party until his retirement and move to California in 1953. He was national chairman emeritus of the SWP when he died in Los Angeles on August 21, 1974.