In 1905 Thomas helped to establish the Intercollegiate Socialist Society. Other members included Jack London, Upton Sinclair, Clarence Darrow, Florence Kelley, Anna Strunsky, Bertram D. Wolfe, Jay Lovestone, Rose Pastor Stokes and J.G. Phelps Stokes. Its stated purpose was to "throw light on the world-wide movement of industrial democracy known as socialism."
Thomas did voluntary social work in New York City before studying theology at the Union Theological Seminary. Influenced by the writings of the Christian Socialist movement in Britain, Thomas became a committed socialist. Thomas was ordained in 1911 and became pastor of the East Harlem Presbyterian Church.
A pacifist, Thomas believed that the First World War was an "immoral, senseless struggle among rival imperialisms". His brother shared his views and went to prison for resisting the draft. Thomas joined with Abraham Muste, Scott Nearing and Oswald Garrison Villard to form the Fellowship of Reconciliation (FOR). In 1917 Thomas, Crystal Eastman and Roger Baldwin established the National Civil Liberties Bureau (NCLB).
In 1918 he founded and edited the World Tomorrow and two years later joined with Jane Addams, Elizabeth Gurley Flynn and Upton Sinclair to establish the American Civil Liberties Union. As well as being associate editor of the Nation (1921-22), he was co-director of the League of Industrial Democracy (1922-37), an organization he had created with Jack London and Upton Sinclair. Thomas was also a frequent contributor to its journal, The Unemployed (1930-32).
Thomas, a member of the Socialist Party, was its candidate for Governor of New York in 1924. After the death of Eugene Debs Thomas became the party's presidential candidate in 1928, 1932 and 1936. Although easily defeated, Thomas had the satisfaction of seeing Franklin D. Roosevelt introduce several measures that he had advocated during his presidential campaigns.
Thomas joined Burton K. Wheeler and Charles A. Lindbergh in forming he America First Committee (AFC) in September 1940 and soon became the most powerful isolationist group in the United States. The AFC had four main principles: (1) The United States must build an impregnable defense for America; (2) No foreign power, nor group of powers, can successfully attack a prepared America; (3) American democracy can be preserved only by keeping out of the European War; (4) "Aid short of war" weakens national defense at home and threatens to involve America in war abroad.
The AFC influenced public opinion through publications and speeches and within a year had over 800,000 members. The AFC was dissolved four days after the Japanese Air Force attacked Pearl Harbor on 7th December, 1941. Although previously a pacifist, Thomas now supported United States involvement in the Second World War. However, he was critical of some aspects of Roosevelt's policies, including the internment of Japanese Americans and big business control of war production.
Thomas was the Socialist Party presidential candidate in 1940, 1944 and 1948. A strong critic of the Soviet communism, Thomas also denounced rearmament and the development of the Cold War. Other issues associated with Thomas during the post-war period included his campaigns against poverty, racism and the Vietnam War.
Thomas wrote several books on politics, including Is Conscience a Crime? (1927), As I See It (1932), A Socialist Faith (1951), The Test of Freedom (1954), The Prerequisites of Peace (1959) and Socialism Re-examined (1963).
Norman Thomas died on 19th December, 1968.