Miller was a member of the state Reconstruction convention in 1867. Upon the restoration of Georgia's congressional representation, Miller was elected as a Democrat to the U.S. Senate on July 28, 1868. However, he did not qualify (and thus was not seated) until February 24, 1871. He served until the end of his term on March 3, 1871.
Miller's tenure in the Senate, at a mere seven days long, ranks (as of 2021) as the third-shortest in American history and the shortest for those who won a full term. The shortest Senate tenure belongs to Sen.Rebecca Latimer Felton from Georgia, who served for only one day from her appointment on November 21, 1922, to November 22, 1922. (The second tenure of Sen.Salmon P. Chase from Ohio is shorter, lasting two days from the beginning of his term on March 4, 1861, to his resignation on March 6, 1861; however, Chase had previously already served a full term from March 4, 1849, to March 3, 1855, so he is not the shortest-serving senator.) The fourth-shortest Senate tenure belongs to Sen.Alva M. Lumpkin from South Carolina, who served three days longer than Miller; he served for ten days from his appointment on July 22, 1941, to his death on August 1, 1941.[5]