The regiment and its predecessor the 1st Pennsylvania Battalion saw action during the Battles of Brooklyn, Valcour Island, Trenton, the Brandywine, Germantown, Monmouth, and Springfield.

By March 30, four of the companies had arrived at the American lines near Quebec, but before the remainder could come up the attack was abandoned and the battalion started the retreat back to New York.

During this time, Congress realized a more substantial national army with enlistments longer than 12 months would be needed to fight the war successfully.

At the Battle of Brandywine, the regiment was part of the force guarding Chadds Ford, Pennsylvania, until the British stormed across the creek and compelled Wayne's Division to withdraw.

By the end of October, the unit had suffered substantially from all the fighting, including the loss of Major Williams who was captured at Germantown.

The few present were able to man a section of the army's first line of defense at Whitemarsh in early December, before moving with the rest of Washington's forces into the legendary winter encampment at Valley Forge.

Here the regiment shared the sufferings of the Continental Line, trained in Von Steuben's new manual of arms and brought itself up to strength.

With France entering the conflict on the side of the new United States in May, the British abandoned Philadelphia and moved across New Jersey to the more easily defended stronghold of New York City.

The young officer, nicknamed "The Irish Beauty" by the ladies of Philadelphia, was a close friend of Anthony Wayne's and was well acquainted with Washington.

The old 2nd Pennsylvania ceased to exist before the final campaign in Virginia and South Carolina, although former members of the regiment were battle casualties at Green Springs on July 6 and Yorktown in October.