Ransdell served in the House from August 29, 1899, to March 3, 1913. He was not a candidate for renomination in 1912, having instead been elected by the Louisiana State Legislature to the United States Senate, prior to the passage of the Seventeenth Amendment to the United States Constitution. In 1918, he defeated future U.S. Senator John H. Overton of Alexandria in a disputed vote. Ransdell won his third term in the Democratic primary election in 1924, having defeated Lee Emmett Thomas, the mayor of Shreveport, 104,312 (54.9 percent) to 85,547 (45.1 percent). Huey Pierce Long, Jr., while himself running for a second term on the regulatory Louisiana Public Service Commission spent more time supporting Ransdell for the Senate than he did his own campaign in which he carried all twenty-eight parishes in his district. Long was particularly motivated by his fierce opposition to Mayor Thomas though Long was then a resident of Shreveport.