John Quincy Marr (May 27, 1825 – June 1, 1861) was a Virginia militia company captain and the first Confederate soldier killed by a Union soldier in combat in the American Civil War. Marr was killed at the Battle of Fairfax Court House (June 1861), Virginia on June 1, 1861. He had been a delegate to the Virginia Secession Convention and ultimately supported secession of Virginia from the Union after initially opposing it.