Smith served in the Revolutionary Army as aide-de-camp to general John Sullivan in 1776. he fought in the Battle of Long Island, was wounded at Harlem Heights, fought at the Battle of White Plains, was promoted to lieutenant colonel at the Battle of Trenton and fought at the Battle of Monmouth and Newport. He was on the staff of General Lafayette in 1780 and 1781, became an adjutant in the Corps of Light Infantry, then transferred to the staff of George Washington.