 Matthews continued to serve in this capacity until 1933.On November 6, 1929, Matthews joined the Socialist Party of America, effectively headed by Norman Thomas, himself a noted pacifist, former clergyman, and FIR associate He was a periodic contributor as a writer for the Socialist and pacifist press, publishing material in the New York weekly "The New Leader" and Norman Thomas's "The World Tomorrow", (where Esther Shemitz, wife of Whittaker Chambers worked).Among other pacifist activities, Matthews served as the Secretary of the Pacifist Action Committee, treasurer of the Joint Peace Council, and on the executive committee of the Emergency Peace Committee in addition to being a member of the Interorganizational Council on Disarmament and the Peace Patriots.