Shopp volunteered for the 6th Regiment, Pennsylvania Reserves on 10 May 1861 in Harrisburg, Pennsylvania. He was mustered into Company E of the 191st Pennsylvania Infantry on 13 May 1861 as a private and fought in the First and Second Battles of Bull Run. He was wounded at the Battle of South Mountain and was treated at a hospital in Frederick City, Maryland. He also fought at Chancellorsville, Arlington Heights, Gettysburg, Wilderness, Spotsylvania Court House, and several other battles in the eastern theatre. During this time, he was shot in the leg by a Confederate sharpshooter. He reenlisted in the Army on 12 February 1864 with veteran status. On 1 April 1865, during the Battle of Five Forks, Shopp captured a rebel flag under heavy fire and killed a Confederate officer.[1][3][4] His Medal of Honor citation reads:[2]
The President of the United States of America, in the name of Congress, takes pleasure in presenting the Medal of Honor to Private George J. Shopp, United States Army, for extraordinary heroism on 1 April 1865, while serving with Company E, 191st Pennsylvania Infantry, in action at Five Forks, Virginia, for capture of flag.
— E. M. Stanton, Secretary of War
Shopp was promoted to corporal on 1 June 1865 and was mustered out of the Army on 28 June 1865 in Washington D.C.[4]