William C. Leath was born around 1841 in Virginia to Lewis and Sarah Leath. His father was a merchant who owned $500 of personal property by 1860. He grew up and attended school in Petersburg, Virginia.
He enlisted in the Confederate army on April 19, 1861, and he mustered in as a sergeant in Company D of the 12th Virginia Infantry. The regiment took part in the Seven Days’ Battles, the Second Battle of Manassas, the Battle of Antietam, the Battle of Fredericksburg, the Battle of Chancellorsville, the Battle of Gettysburg, and the siege of Petersburg. He was promoted to 1st lieutenant in February 1863. He was wounded on August 19, 1864, and Union forces captured him. He disappeared from the documentary record afterward.