Once in America, Mercer enlisted in the army of the Hanoverian king, George III, whom he had sought to overthrow during the uprising in Scotland. During the Seven Years’ War, he first served in General Edward Braddock’s disastrous expedition of 1755, in which he was wounded, and then again with Lieutenant Colonel John Armstrong’s army at the raid of Kittanning in 1756.
From 1760 to 1775, Mercer worked as an apothecary and practiced medicine in Fredericksburg, Virginia. When the colonies took up arms against the British, he quickly returned to his rebellious roots. When first commissioned as a captain in the Continental Army, Mercer was charged with leading the Independent Company of the Town of Fredericksburg. He was soon made a lieutenant colonel, commanding a militia battalion. By December 1775, he was a full colonel and the first commander of the 3rd Virginia Regiment, with luminaries including James Monroe and John Marshall under his command. General George Washington personally requested Mercer’s promotion to brigadier general in June 1776.
Six months later, Mercer led a brigade during the Battle of Princeton. Although famed medic Benjamin Rush tended to Mercer’s seven bayonet wounds, he could not save his medical colleague and fellow Patriot. Mercer died in the Thomas Clarke House on the eastern end of the battlefield, nine days after the battle ended in victory for the Patriots.
