After his education concluded, Harrison traveled to Europe, and began building mercantile connections, as well as his fortune. However, the American Revolutionary War prompted him to return home to Virginia, as he strongly wanted to aid his father and the Patriot cause. From 1774 to 1775, he was a member of the Charles City County Committee, as well as a member of the Virginia House of Delegates. During the war, he became the Deputy Paymaster General of the Continental Army, helping finance and pay the Continental Army during the Southern theater.