John Selby Mackay, banker and coalmaster in Grangemouth succeeded his grandfather, John Selby, in the office of Collector of canal dues for the Forth and Clyde Canal Company at Grangemouth. John Selby MacKay was also manager of the Grangemouth branch of the Commercial Bank in or before1836. He also became Treasurer and a Director the Grangemouth Gas Company . He was closely involved in Grangemouth Coal Company, Grangemouth Traders Building Company and Grangemouth Towing Company as well as owner of several heritable properties and owner of shares along with his brother, George Gray MacKay, in several ships. He was also collector of subscriptions to the local Volunteer Force from 1860. He was the first Chief Magistrate for Grangemouth, from 1872 to 1878, there being no Provost at the time.