The 84th Pennsylvania Infantry was organized at Huntingdon, Pennsylvania and Camp Curtin (in Harrisburg) beginning October 1861 and mustered in on December 23, 1861, for a three-year enlistment under the command of Colonel William Gray Murray.
The regiment was attached to 1st Brigade, Lander's Division, Army of the Potomac, to March 1862.
4th Brigade, Shield's Division, Department of the Rappahannock, to June 1862.
4th Brigade, 2nd Division, III Corps, Army of Virginia, to September 1863.
2nd Brigade, 3rd Division, III Corps, Army of the Potomac, to June 1863.
Moved to Hancock, Md., December 31 – January 2, 1862, then to Bath.
Pope's Campaign in northern Virginia August 16 – September 2.
Duty at Arlington Heights, defenses of Washington, Whipple's Command, until October.
Guarding Corps' trains during battle of Gettysburg July 1–3.
Mine Run Campaign November 26 – December 2.
Demonstration north of James River at Deep Bottom July 27–29.
Demonstration north of the James at Deep Bottom August 13–20.
Strawberry Plains, Deep Bottom, August 14–18.
Peebles' Farm, Poplar Grove Church, September 29 – October 2.