John Munro's father was of modest means and unable to purchase a commission for his son. As a Sergeant-Major of the 48th (Northamptonshire) Regiment of Foot, John came to North America in 1756, seeing active service in the Seven Years' War at the Battles of Louisburg and Quebec. Following the war, he was disbanded and received extensive land grants for his military service east of the Hudson River at Schenectady, Albany County, New York. This estate, which he named "Fowlis", soon came to encompass over 11,000 acres of land. He became a merchant and rapidly prospered in business, particularly in the fur trade, becoming a close lifelong friend of Simon McTavish, who sponsored one of his sons. Munro was an elder of the English Presbyterian Church in Albany, and a Magistrate for the County of Albany and the County of New York.