Hiram Rhodes Revels was sworn in as the first African American U.S. Senator on February 25, 1870. He had been in politics only two years, first serving as a Natchez alderman and then as the Adams County representative to the Mississippi State Senate. The State Senate elected him to the U.S. Senate on the strength of his oratory in the prayer he gave at its opening session. (U.S. Senators were not elected by popular vote until the ratification of the 19th Amendment in 1913.)

Read more here http://history.house.gov/…/R/REVELS,-Hiram-Rhodes-(R000166)/