Entrepreneur. Based in Dundee, Mackay was one of a syndicate of Dundee businessmen who bought the Matador Land and Cattle Company of Texas (USA) in 1882. The company had been established in 1879, but looked overseas for venture capital. Mackay was first secretary, board member (1912-36) and then chairman (1915-36) of this company, which held around 607,290 ha (1,500,000 acres) of land. The company returned a healthy dividend each year and when it was sold in 1951, its value had increased more than 30-fold from when the Dundee syndicate bought it.
Interestingly, Mackay is known to have purchased a painting called The Matador, by Scottish Colourist Francis Campbell Boileau Cadell (1883 - 1937).