The Southern Tenant Farmers' Union was an interracial organization of tenant farmers, sharecroppers, and wage laborers that emerged from northeastern Arkansas in the mid-1930s. The STFU became the most important social action on the part of landless agricultural workers during the Great Depression and one of the most significant critics of the New Deal and the Agricultural Adjustment Administration. This study examines the STFU as a dramatic expression of the Social Gospel in the South during the 1930s and as a representation of the cooperative work of radical and moderate American leftists during the interwar period. From its inception, the STFU faced the violent opposition of planters and local authorities, yet the union managed to survive until the end of the decade as a result of talented leadership, the effectiveness of its organizational strategy, and the patronage of influential leftist leaders around the nation. The plight of the sharecroppers attracted the concern and attention of the eastern liberal establishment, Socialist leaders such as Norman Thomas, and the Communist Party. However, southern progressive leaders such as Harry Leland Mitchell, a former sharecropper turned political radical from west Tennessee, always led the union. The STFU also drew members of a new generation of southern seminary-trained social activists. These "Radical Prophets," through work with southern labor and national organizations such as the NAACP and the Fellowship of Reconciliation, injected the Social Gospel theology taught by social activists and university professors such as Alva Taylor at Vanderbilt University with a Marxist inspired desire to revolutionize southern economic and social institutions in keeping with the philosophy of modern theologians such as Reinhold Niebuhr. Southern labor leaders, radical ministers, regional black leaders, and white and black country preachers, combined in the STFU, and the potent mixture allowed the union to quickly organize thousands of the nation's most impoverished and disenfranchised in a valiant though ill-fated effort to reform southern society. This thesis also presents the STFU as a microcosm of the dissolution of the American left consensus as the Great Depression came to an end. By the early 1940s, the union had all but disappeared after having reached a peak of 35,000 members. Although the pressures associated with affiliation with an international union and the changing demographics of the Delta South were the direct causes of the union's failure, ideological rifts between the radical and moderate leaders of the union, as closely observed below in the split between the "Radical Prophets" Howard Kester and Claude Williams, hastened the STFU's demise. By analyzing the letters and first-hand accounts of STFU leaders and organizers in the context of radical Christianity and leftist political and social thought, this study provides a new perspective concerning the STFU which addresses the place of the union in 1930s intellectual history and as a manifestation of the often overlooked radical progressive tradition that existed in the South during the period.