Finegan's second brigade, consisting of the Thirty-second Georgia, Sixty-fourth Georgia, First Georgia Regulars, Twenty-eighth Georgia Artillery Battalion, First Florida Battalion, and the Georgia Light Battery, was commanded by Colonel George P. Harrison. This young officer, still one month short of his twenty-third birthday, had already established a solid military reputation. In January 1861, while a student at the military institute at Marietta, Georgia, he took part in the capture of Fort Pulaski and was commissioned a second lieutenant in the First Georgia Regulars. After serving in Virginia during the winter of 1861-1862, Harrison returned to Georgia and took command of the Fifth Regiment of Georgia State Troops.
Harrison then organized and was appointed colonel of the Thirty-second Georgia Infantry, a regiment he commanded throughout the 1863 siege of Charleston. During the defense of the city Harrison and his unit were stationed at various locations, including James Island, Fort Johnson, Morris Island, John's Island, Fort Sumter, and Fort Wagner. At Fort Wagner he contributed significantly to the bloody repulse of the July 22, 1863, Union attack. Despite his age, by early 1864 Harrison had developed into a seasoned combat commander, displaying the aggressiveness of youth and strong leadership traits, coupled with coolness under fire. As yet untried in commanding a brigade in battle, few doubted that he would continue to maintain his solid reputation.
Harrison commanded the second Confederate infantry brigade at Olustee. It consisted of the First Florida Battalion, First Georgia Regulars, 28th Georgia Heavy Artillery Battalion (also known as Bonaud's Battalion and serving as infantry), 32nd Georgia, 64th Georgia, and Guerard's Battery. The brigade suffered official casualties of 50 killed, 406 wounded and four missing.
After a competent performance at Olustee, Harrison continued in brigade command for the rest of the war. Although some works cite him as him as being promoted to brigadier-general in 1865, he apparently was never formally
Harrison was elected as a Democrat to the Fifty-third Congress to fill the vacancy caused by the resignation of William C. Oates. He was reelected to the Fifty-fourth Congress and served from November 6, 1894, to March 3, 1897. After his final term in Congress, he resumed the practice of law in Opelika, Alabama. He served as delegate to the State constitutional convention in 1901. Harrison again served in the Alabama State senate in 1900 and 1902. Harrison served as general counsel for the Western Railway of Alabama and as Division counsel for the Central of Georgia Railway. He was major general of the Alabama Division of the United Confederate Veterans.advanced to that rank. In the post-war years, Harrison worked as a lawyer in Alabama.