He represented Cape Breton in the House of Commons of Canada from 1872 to 1878 as a Conservative and then Liberal member.
[1] He was born in Halifax, Nova Scotia,[1] the son of William McKay, and was educated there.
Mackay was called to the Nova Scotia bar in 1859 and named a Queen's Counsel in 1872.
He ran unsuccessfully for a seat in the Nova Scotia assembly in 1867 and 1871 before he was elected to the House of Commons.
[2] After his defeat by Hugh McLeod in 1878, he was an unsuccessful candidate in each subsequent federal election until his death in 1886[1] in Sydney.