Born in Albemarle County, Virginia, around 1815, John Barnett was owned by James Campbell. Campbell purchased Barnett from a man named Jocky Billy Barnett. Before the war, John Barnett lived in Gerrard County, Kentucky, with Campbell. Barnett married a woman named Lavinia, with whom he had seven or eight children. Two of their children are mentioned by name in his pension records: Margaret Helms and George Denny. Lavinia died at an unknown date well before the war. Following Lavinia’s death, Barnett married a woman named Lucy in 1836.

On April 20, 1865, 50-year-old Barnett enlisted as a private in the Union army at Camp Nelson, Kentucky. Standing at 5 feet, 9 inches tall, with black hair and eyes, his service record describes Barnett’s complexion as black and his occupation as farmer. Five days later, on April 25, Barnett mustered into Company D of the 124th USCT Infantry Regiment at Lexington, Kentucky. Barnett’s regiment primarily participated in garrison and guard duty in the Department of Kentucky. Barnett did not serve long before he fell ill. On July 20, 1865, Barnett died of cholera morbus at the General Hospital in Camp Nelson, Kentucky. He was buried in the national cemetery at Camp Nelson. After the war, his widow Lucy received a pension for his service.