John Mackay (1774–1841) was a well known and successful ship master and early industrialist in Boston, Massachusetts. John Mackay was born in Boston and he participated in the Mackay family business of shipping started by his father and uncle. He partnered with and financed Alpheus Babcock and Jonas Chickering in early piano manufacturing by using some of his legacy from his wealthy uncle Mungo Mackay.
John Mackay was the son of the Scottish immigrant Alexander Mackay (1747–1801) and his Boston born wife Ruth Decoster(1742–1833). John Mackay learned the shipping trades as a young man from his father and his uncle Mungo Mackay. John Mackay became a member of the Boston Marine Society on February 3, 1796. During this early period he sailed ships to foreign ports to obtain cargo for the Boston market. He was aided by the trade contacts his uncle Mungo Mackay had built up, and by some of the sons of Mungo Mackay who were located on islands in the Caribbean as agents. He also had an aunt and several cousins in London.
In November 1798 the Massachusetts Mercury newspaper carried an announcement of the eminent sailing for London of the new ship Galen with John Mackay as Master. John Mackay was described as an "old experienced Master".
John Mackay's father died in 1801, when John was 27. He assumed the responsibility for his father's business and the care of his mother and sister Jennet. There is a scant record of a brother Mungo, but no birth or death record has been found.
John Mackay married Mungo Mackay's youngest daughter Fanny (1875-1870) in January 1807. They were first cousins. Fanny lived with her mother and father on Cambridge Street in the developing West End of Boston. John lived in his parents' house on Federal Street, and the couple moved to a home on Hancock Street in the West End. John Mackay and his partner Thomas Prince had a store at 66 State Street, near Faneuil Hall.
Their first child was Frances, born in 1807, who died in 1858. Their second child was Caroline, born in 1810, who died in 1888. Their third and final child was William Harvey, born in 1817, and who died in 1850, all in Boston.
With the death of John Mackay's uncle Mungo Mackay in 1811, John Mackay became the executor of his estate, sharing duties with Samuel Parkman and Mungo's widow Ruth. It was a large and complex estate and it took many years to settle all the details. His mother in law, Ruth Coney Mackay, died in 1820, adding to his estate and legacies.