This thesis offers a comparative biography of the Louisiana politician-turned presidential hopeful Huey Long and the Socialist Party of America leader Norman Thomas. The focus is on Long and Thomas’s activities during President Franklin D. Roosevelt’s first presidential term, especially insofar as the men were rivals. The thesis draws on archival sources obtained from Tulane and Louisiana State University as well as the Louisiana Historical Center pertaining to Huey Long and a collection at the New York Public Library for information on Thomas. Long’s memoir Every Man a King and Thomas’s unpublished autobiography, Thomas’s oral history preserved by Columbia University’s Oral History Project, and secondary sources provided invaluable information. The first two chapters retrace Huey Long’s rise to power in Louisiana and at the national level. Long was a transformational, progressive figure whose rabble rousing and prioritization of economic over cultural grievance upended Bourbon Democratic rule over Louisiana and contributed to the overthrow of the American government’s laissez faire, non-interventionist consensus in response to the Great Depression. Chapters three and four follow Thomas’s rise from middle-class respectability as a Presbyterian minister to Socialist radical. Thomas rose to a position of dominance over the Socialist Party, the American 20th century’s most formidable third party. Thomas’s leadership revitalized the Party and positioned it to jockey for influence with Huey Long and FDR during the Depression era. Long and Thomas’s rivalry influenced them to pressure President Roosevelt. In as much as Long and Thomas’s Socialists shaped the New Deal, they left an indelible mark on American social democracy.