On October 1, March was forced to resign due to illness and was succeeded by Lt. Col. Albert Magilton of the 2nd Reserves.

After Fredericksburg, the 2nd Brigade, including the 4th Pennsylvania Reserves, was transferred from the Army of the Potomac in early 1863 to serve in the defenses of Washington, D.C.

In 1864, it served in West Virginia, fighting at the Battle of Cloyd's Mountain, where the regiment's colonel, Richard H. Woolworth, was mortally wounded.

The depleted regiment was mustered out in Philadelphia on June 15, 1864, when its original three-year term of enlistment expired.

Men who reenlisted and those replacements whose enlistments had not yet expired were transferred to the 54th Pennsylvania Volunteer Infantry on June 8.