Frederick Mackenzie was born around 1731, likely in Dublin, Ireland, the only son of Scottish merchant William Mackenzie and Mary Ann Boursiquot, who was of French Huguenot descent. Little is known of Mackenzie's life until, in 1745, he received his first commission in the 23rd Regiment of Foot, also known as the Royal Welch Fusiliers. During the War of the Austrian Succession, his regiment served at the battles of Dettingen, Fontenoy, and Lauffeld. They also fought at the battles of Minden, Warburg, and Wilhelmsthal in the European theater of the Seven Years' War. After traveling to North America in 1773 and to Boston with his regiment in August 1774, Mackenzie was promoted to captain and served as major of brigade under General William Howe in Halifax. He served as deputy adjutant-general for the army under Henry Clinton from 1778-1782 (obtaining majority in 1780) and Guy Carleton from 1782-1783. In 1787, he became lieutenant colonel of the 37th Regiment of Foot, and in 1794, he raised and led the 1st Exeter Volunteers, in the face of a potential Napleonic invasion. He later became assistant barrack master general at British headquarters and secretary of the Royal Military College. He died in 1824 in Teignmouth, Devon, England.