Born in Queen City, Missouri, he moved to Minneapolis when young and became a Republican, but during the Great Depression he joined the Teamsters and the Communist League of America. He was one of the initiators of a general strike in Minneapolis, and for a while worked full-time as a union organiser, but quit in 1939 to work for the new Socialist Workers Party (SWP).
For opposing World War II, he was convicted of treason and from 1944 served a year in jail. After his release, he became the editor of the SWP's newspaper, The Militant. From 1948 to 1960 he was the SWP's candidate for President of the United States, and succeeded James P. Cannon as national secretary of the party in 1953. He retired in 1972 and remained in the party even after it expelled large numbers of Trotskyists under Jack Barnes' leadership.