In 1861, the American Civil War broke out when Barnes was just 16 years old. Barnes joined the Union army as a volunteer soldier. Barnes’s earlier experients in telegraphy earned him a position in the Military Telegraph and Engineering Corps of the Union army. Barnes would serve for the entire duration of the war. During his service, he would spend a portion of his enlistment as the secretary to Brigadier General Nathaniel Lyon. Barnes would leave the army at the age of 20.
During Barnes’s time in Arkansas, Barnes married Elizabeth Mary Bartlett of North Adams, Massachusetts, in Little Rock on June 4, 1868. Barnes would gain a friendship with the powerful Clayton family, most notably former Governor of Arkansas and (then) Senator Powell Clayton. Through his friendship with Clayton, Barnes was appointed, by President Benjamin Harrison, Receiver of the United States Land Office at Guthrie in 1890 with the opening of Oklahoma Territory. He would hold that position for four years.
Barnes was a member of the Episcopal Church, serving as a senior warden of the Guthrie church for many years. He was an active affiliate of both the Scottish and York rites of the Masonic fraternity. It was also during his tenure as Receiver, Barnes would study law and passed the bar exam in 1893. He would serve as a member of the 3rd and 4th sessions of the Oklahoma Territorial Legislature, serving from 1895 to 1897. During the 3rd session, Barnes would serve as the Legislature’s speaker.
During Governor Barnes’s four year term, little happened that was of great note. The only point of interest was Governor Barnes’s fight against a growing government. Governor Barnes defeated the attempts of the 6th Legislature to create numerous additional territorial institutions. This expansion of territorial government was justified by the Legislatures by the rapidly growing idea for the formation of the State of Oklahoma. Governor Barnes promptly vetoed this legislation.
Governor Barnes’s term in office ended on April 15, 1901 when William Miller Jenkins took the oath of office as his successor.
Barnes second marriage was to divorcee Rebecca Cagle Forney. He married her in Chicago in 1910. After the marriage, the two moved to Leavenworth, Kansas, where Rebecca served as an instructress in a girl's seminary. Once again, Barnes’s interest in telegraphy served him. He would become a postal telegraph operator in Leavenworth.
In his late years, his health began to fail. This caused him to move to New Mexico, where he died at Albuquerque on February 18, 1925. His body was returned to Guthrie and interred in the Summit View Cemetery.