Robert Byington Mitchell (April 4, 1823 – January 26, 1882) was a brigadier general in the Union Army during the American Civil War and the Governor of the New Mexico Territory from 1866 to 1869.

[2] After the start of the Civil War, Mitchell served as the Adjutant General of Kansas from May 2, 1861, to June 20, 1861.

[2] After recovery, U.S. President Abraham Lincoln appointed him as a brigadier general to rank from April 8, 1862, and he was given command of a mixed brigade at Fort Riley.

[2] During the Chickamauga campaign, Mitchell served as George H. Thomas's Chief of Cavalry for the Army of the Cumberland.

According to some sources, this was due to severe wounds which incapacitated him from field duty but this is contradicted in the Official Records by Mitchell's own correspondence.

He was often absent from the territorial capital Santa Fe, without explanation, forcing the legislature to forward bills it had passed to Washington, D.C., for approval of the United States Congress.