James B. Cowan was born around 1826 in Virginia. By 1860, he was working as a brick mason in Bastrop, Texas, and he owned $1,000 of personal property.
He enlisted in the Confederate army on September 7, 1861, and he mustered in as a private in Company D of the 8th Texas Cavalry. The regiment took part in the Battle of Shiloh, the Battle of Perryville, and the Battle of Chickamauga. He remained in the army until at least February 1864.
He returned to Bastrop after leaving the army, and he died there in 1867.