After several years with the Canada national team, including playing at two World Championships and the 1968 Winter Olympics, winning a bronze medal, MacMillan made his NHL debut in 1970 with the Toronto Maple Leafs.

MacMillan was born on March 7, 1943, in Charlottetown, Prince Edward Island (PEI),[1] where he grew up and excelled at a variety of sports, including hockey, rugby, and track.

He was selected in the 1972 expansion draft by the Atlanta Flames, playing in a checking role with the team during its inaugural season.

The following season, he was hired by the Colorado Rockies to serve a dual role as general manager and head coach.

After one season, he was relieved of his coaching duties, but after the team moved and became the New Jersey Devils in 1982, he returned to a capacity behind the bench.

[7][8] He then returned home in Prince Edward Island and coached the UPEI Panthers for many years; in 1991, he guided the team to a conference title and a berth in the CIAU University Cup Final Four.