 He was a chief Liberal Party strategist and fundraiser and was an advisor to three Liberal Prime Ministers - William Lyon Mackenzie King, Louis St. Laurent and Lester Pearson and had also known Sir Wilfrid Laurier, a friend of his father, as a youth.His father was Judge Duncan Byron MacTavish.He was educated in Ottawa and at Queen's University and Osgoode Hall Law School before being admitted to the bar in 1926.