Bristow studied law in his father's office and was admitted to the bar in 1853. He served in the Kentucky state Senate (1864–65) and sought the reelection of President Abraham Lincoln. After the war, as U.S. attorney for the Kentucky district (1866–70), he worked for the protection of blacks against the Ku Klux Klan. In 1870 President Ulysses S. Grant (Grant, Ulysses S.) made him the first solicitor general of the United States. Appointed to the treasury post by Grant in 1874, Bristow broke up the Whiskey Ring. Its members fought back by influencing Grant to believe that Bristow was using his office for political gain. He resigned under presidential pressure and returned to the practice of law. At the 1876 Republican convention in Cincinnati, Bristow was a strong contender for the presidential nomination but chose finally to bow out of a deadlock by throwing his support behind Rutherford B. Hayes. He thereafter (from 1878) practiced law in New York City.