A Liberal, Mackay defeated Progressive incumbent Clifford Barclay[4] by 18 votes in the riding of Springfield.
After a brief period in which James Breakey led the parliamentary caucus, Mackay was chosen[1] over Fred C. Hamilton as party leader in 1931.
Mackay attempted a comeback in 1945, but lost to CCF candidate George Olive[4] by over one thousand votes.
As well as being a politician, MacKay was known by many as a prominent local physician in the town of Transcona,[1] with a reputation for kindness and a great sense of humour.
He remains a community hero and his commitment to the Transcona area was honoured in his 2005 nomination as "The Greatest Transconian".