Johnson Kelly Duncan was born in Chanceford, York, Pennsylvania March 19th 1827. He received an appointment to the United States Military Academy, graduating 5th out of the class of 1849. He started his military career as a Second Lieutenant in the Third Artillery with fighting against the Seminole Indians in Florida. In 1855 with the rank of First Lieutenant, Duncan left the army and moved the Louisiana. He worked in New Orleans as an architect, surveyor and the Chief Engineer of the Board of Public Works.
When the Civil War started Duncan sided with those of his southern home, and enlisted in the Confederate service, becoming the Colonel of the 1st Louisiana Artillery. He was promoted to Brigadier General January 7th 1862, and placed in command of the defenses of the Lower Mississippi. When Union Admiral David Farragut captured Fort Jackson on April 28th 1862, Duncan became a prisoner of war. After a prisoner exchange on August 27th 1862, Duncan was assigned to Confederate General Braxton Bragg as his Chief of Staff. While on this duty, he contracted Malarial and died December 18th 1862 in Knoxville, Tennessee. Duncan is buried in the Confederate Cemetery in Franklin, Tennessee.