In 1890, Barber was elected Secretary of State of Wyoming as a Republican. Just eleven months later, however, Governor Francis E. Warren resigned to take up a United States Senate seat, and Barber was catapulted to the position of Acting Governor on November 24, 1890, at the age of just 30. During his administration, he called out state troops to quell a Pine Ridge Indian outbreak and asked for federal assistance with the Johnson County War between cattlemen (WSGA) and cowboys (small time ranchers) in Johnson County in 1892. When John E. Osborne was elected on January 2, 1893, Barber continued on as Secretary of State under Osborne until his term ran out in 1895 and then returned to Cheyenne and his practice.