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.
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 and his partner Thomas Prince had a store at 66 State Street, near Faneuil Hall.
When Mungo Mackay's widow Ruth Coney died in 1820 at age 77 in the mansion house on Cambridge Street in Boston's West End she left, in addition to her daughter Fanny, a son Samuel who lived in the Barbados, a son Joseph who lived with her and no other direct male descendants other than the members of the family of Samuel Hunt who had married her daughter Ruth and had 12 children.
George Mackay Dowling is listed as a Member of the Boston Sea Fencibles in the August 1814 Signal Roll.
In 1815, the firm known as "Boston Musical Instrument Manufactory" was opened at 6 Milk Street by the Hayt brothers, Babcock and Appleton.
Prince took in William M. Goodrich, formerly of the Boston Musical Instrument firm, as a third partner, and they started manufacturing church organs.
[8] G. D. Mackay's will, which had been written in 1823, and probated in 1825, inventoried many items of interest to piano manufacturing in the United States.
Of the several completed instruments in the factory at the time of G. D. Mackay's death several were sold to people in the Boston area including Harrison Gray Otis.
John Mackay partnered with Jonas Chickering in a piano manufacturing enterprise in Boston, starting in 1830.
[11] John Mackay died at sea in 1841 while on a voyage to South America, apparently to procure wood for his piano cases that he was manufacturing with Jonas Chickering.
From 1841 until 1853 Chickering gradually bought out the remaining members of the Mackay family, although a devastating fire in 1852 cost all partners a large sum of money.
(p. 271)John Mackay of whom I have spoken although reputed to have no practical knowledge of piano or its details took out a patent for a new method of covering and boring the shank holes of hammer heads on August 14, 1828.
John Mackay was originally a ship merchant and bore the title of Captain He acquired some knowledge of and taste for the piano business while trading between and England and Boston in past years, carrying general merchandise after the manner of sea captains referred to in New York chapters and possessed considerable wealth with which he backed up Babcock.