Following the completion of the trial, in October 1865, Burnett asked to be mustered out on December 1, 1865, which was granted. Senator John Sherman and Holt asked for him to be appointed a brevet brigadier general, which he accepted in May 1866. On January 13, 1866, President Andrew Johnson nominated Burnett for appointment to the grade of brevet brigadier general of volunteers, to rank from March 13, 1865, and the United States Senate confirmed the appointment on March 12, 1866.