Douglass was born in Thomaston, Georgia, October 5, 1830. After graduation from the University of Georgia, he practiced law in Cuthbert, Georgia. On June 19, 1861, he was commissioned captain of Company E, 13th Georgia. He was promoted to Lt. Colonel July 8, 1861, and to full Colonel February 1, 1862. Douglass was killed at the battle of Antietam while commanding Lawton's brigade south of the section of the battle known as the Cornfield on September 17, 1862. He is buried in Rosedale Cemetery, Cuthbert.
- "Ewell's Division, Jackson's Left Wing, Army of Northern Virginia, August 1862". civilwarintheeast.com. Retrieved 2015-06-18.
- "Col Marcellus Douglass". antietam.aotw.org. Retrieved 2015-06-18.
- "Col Marcellus Douglas, d1862". douglashistory.co.uk. Retrieved 2015-06-18.
- Edwin C. Bearss; James M. McPherson (June 2007). Fields of Honor: Pivotal Battles of the Civil War. National Geographic Society. pp. 97–. ISBN 978-1-4262-0093-9.