John Munn was born around 1830 in North Carolina. He married Arritta Jernigan around November 1850, and they had at least four children: Daniel, born around 1852; Catherine, born around 1854; John, born around 1859; and Neil, born around 1863. They lived in Dale County, Alabama, and he worked as a farmer. By 1860, he owned $1,000 of real estate and $400 of personal property.
He enlisted in the Confederate army on August 15, 1862, and he mustered in as a private in Company E of the 15th Alabama Infantry. The regiment took part in the Second Battle of Manassas, the Battle of Antietam, the Battle of Fredericksburg, the Battle of Gettysburg, the Battle of Chickamauga, the Overland Campaign, and the defense of Petersburg. He was wounded at Chickamauga on September 20, 1863, and again at Darbytown Road on October 13, 1864. Union forces captured him after the latter battle, and he died of chronic diarrhea at Point Lookout, Maryland, on July 9, 1865.