He was born in Riverton, Nova Scotia, the son of Daniel MacKay and Christy Ann Robertson. MacKay was educated in Stellarton. In 1897, he married Margaret Fraser. MacKay was mayor of Westville in 1907. He ran unsuccessfully for a seat in the provincial assembly in 1906. MacKay was an unsuccessful candidate for a seat in the House of Commons in 1917 and 1925.