The unit has the distinction of being the first Union Army infantry regiment to open fire at the Battle of Gettysburg.

The 56th Pennsylvania Infantry was organized at Camp Curtin in Harrisburg, Pennsylvania in Fall 1861 and mustered in March 6, 1862 for a three-year enlistment under the command of Colonel Sullivan Amory Meredith.

Doubleday's Brigade, Department of the Rappahannock, to June 1862.

2nd Brigade, 3rd Division, III Corps, Army of Virginia, to September 1862.

2nd Brigade, 1st Division, I Corps, Army of the Potomac, to March 1864.

3rd Brigade, 2nd Division, V Corps, Army of the Potomac, to September 1864.

Guarded the railroad bridge at Potomac Creek May 21–27.

Pope's Campaign in northern Virginia August 16 – September 2.

Brandy Station and Beverly Ford June 9.

Mine Explosion, Petersburg, July 30, 1864 (reserve).

Poplar Springs Church September 29 – October 2.

Boydton Plank Road, Hatcher's Run, October 27–28.

Warren's Raid on Weldon Railroad December 7–12.