The regiment was raised in Jamaica by Colonel Edward Trelawney as Edward Trelawney's Regiment of Foot in 1743 from eight independent local companies. The regiment was ranked as the 63rd Regiment of Foot in 1747 and re-ranked as the 49th Regiment of Foot in 1751. The regiment landed in Ireland in 1764 and remained there until embarking for Newfoundland in 1772. The regiment moved to Boston in June 1775 for service in the American Revolutionary War. It fought at the Battle of Long Island in August 1776, the Battle of White Plains in October 1776 and the Battle of Fort Washington in November 1776. It went on to take part in the Philadelphia campaign, seeing action at the Battle of Brandywine in September 1777, the Battle of Paoli later that month and the Battle of Germantown in October 1777. In summer 1778 and took part in the British victory at the Battle of St. Lucia in December 1778 before returning to Ireland in 1780. In 1782, the regiment received a county distinction becoming the 49th (the Hertfordshire) Regiment of Foot.