Samuel P. Harris was born around 1826 in Hancock County, Georgia.
He enlisted in the Confederate army on July 15, 1861, August 7, 1861, and he mustered in as a private in Company E of the 15th Georgia Infantry. According to his service records, he was 5 feet, 8 inches tall, with black hair and dark eyes. The regiment took part in the Seven Days’ Battles, the Second Battle of Bull Run, the Battle of Antietam, the Battle of Fredericksburg, the Battle of Chancellorsville, the Battle of Gettysburg, the Battle of Chickamauga, the Overland Campaign, the siege of Petersburg, and the Appomattox campaign. In November 1861, he declared that, "if Lincoln were to attack us at Centreville [Virginia] with 300000 men we could whip and kill so many of them that they would never show their heads again in Virginia."
He eventually earned a promotion to corporal and then to sergeant, but he was reduced to the ranks by April 1863. He remained devoted to the Confederate cause. As General William T. Sherman marched through Georgia, Harris “fear[ed] the people of [Georgia] will suffer more from the Yankees than they have ever done before. But God grant we may yet ruin the Yankee army…The army of Gen Lee is still hopefull.” He remained in the army until at least February 1865.