In 1917, Randolph and Chandler Owen founded The Messenger with the help of the Socialist Party of America. It was a radical monthly magazine, which campaigned against lynching, opposed U.S. participation in World War I, urged African Americans to resist being drafted, to fight for an integrated society, and urged them to join radical unions. The Department of Justice called The Messenger "the most able and the most dangerous of all the Negro publications." When The Messenger began publishing the work of black poets and authors, a critic called it "one of the most brilliantly edited magazines in the history of Negro journalism."
Randolph's first experience with labor organization came in 1917, when he organized a union of elevator operators in New York City. In 1919 he became president of the National Brotherhood of Workers of America, a union which organized among African-American shipyard and dock workers in the Tidewater region of Virginia. The union dissolved in 1921, under pressure from the American Federation of Labor.