He also served on the national committee of the American Youth Congress (AYC) and the National Student League (NSL), two of the Communist Party's efforts to make inroads with American students. Matthews was also a speaker for the Unemployed Leagues, the CPUSA-sponsored mass organization directed at the unemployed, International Labor Defense, the party's legal defense organization, and the Teachers' Anti-War Conference, as well was a member of the national committees of the National Tom Mooney Council of Action and the National Scottsboro Committee of Action. Matthews visited the Soviet Union no fewer than five times during the late 1920s and early 1930s. He wrote extensively for the Communist press, contributing material to the "Daily Worker" (including a front page denial of the reality of the massive famine in the Ukraine in 1932–33), "Soviet Russia Today" (edited by Jessica Smith, wife first of Harold Ware and then of John Abt), and "The New Masses" (whose editors included Whittaker Chambers. Matthews' participation in organizations closely linked to the Communist Party led Richard Rovere to derisively describe Matthews as "the world's champion fellow traveler, joining Communist fronts as compulsively as a pie-eating champion eats pies," according to Richard Rovere. Although conservative public intellectual William F. Buckley Jr. contended that J. B. Matthews himself coined the term "fellow traveler", in reality the phrase was an anglicization of a Russian word in common currency since the time of the Russian Revolution of 1917 — "poputchik" (literally: "one who walks the same path"). Regardless of this misconception of the phrase's origin, Matthews unquestionably helped popularize the term in so describing himself in the title of his repentant 1938 memoir. Matthews became among the first anti-communist informers to testify before House Special Committee on Un-American Activities, commonly known as the Dies Committee. Matthews went on to become the research director for the Dies Committee, opening up a new career for him as a professional anti-communist investigator. With the Dies Committee seemingly scheduled for termination in 1944, Matthews scrambled to preserve the material that he had compiled through an official committee publication. Over 2,100 pages were rushed to the printer and published in seven volumes, which together were known as "Appendix IX" of the committee's report. "Appendix IX" included a massive list of 22,000 names of individuals and their organizational connections to "subversive" organizations—many of whom were not themselves communist.