In November 1869, Fountain won a seat as a Republican in the Texas Senate, serving in the Twelfth and Thirteenth Texas Legislatures. He was elected as president "pro tempore" during the second session of the Twelfth Legislature and served as Lieutenant Governor "ex officio" at the same time, as the office was vacant. Fountain's most notable accomplishment was pushing through the bill that re-established the Texas Rangers, which had been abolished after the Civil War. Fountain's Radical Republican views angered Texas Democrats and he was challenged to several duels, resulting in him killing at least one man, Frank Williams.