Born around 1854, Middleton came to Lincoln County in the New Mexico Territory from Texas in the mid-1870s and went to work for John Tunstall. Described as a heavyset, swarthy man with black hair and eyes and a large handlebar mustache, Middleton was known as a first-rate cowboy as well an excellent fistfighter and pistol marksman.
Middleton was close enough to John Tunstall to hear his last words just before he was shot down by Dolan gunmen William Morton, Jesse Evans and Tom Hill on February 18, 1878. After this, Middleton participated in most major Lincoln County Regulators operations of the Lincoln County Wars. That included the murder of Sheriff William Brady on April 1, 1878.
Three days later, Middleton would be dangerously wounded in the chest during the gunfight with Buckshot Roberts at the Gunfight at Blazer's Mill. Amazingly, he survived his wound and resumed his place with the Regulators once he recovered. By autumn of 1878, the war was over and Middleton and the last of the Regulators split up.
John Middleton's ultimate fate is unclear; some say he remained in the area, dying of smallpox on November 18, 1882 in San Lorenzo, New Mexico. Others accounts say he moved to Kansas, where he married and worked as a cowboy, dying in 1885, either by drowning in a stream or from the effects of his chest wound sustained years earlier at Blazer's Mills.
- Billy the Kid: A Short and Violent Life, by Robert M. Utley, University of Nebraska Press, 1989.