Led by MacInnis' 31 points, the Flames won the first Stanley Cup championship in their history in 1989. He had four goals and five assists in six games in the final series against the Montreal Canadiens en route to winning the Conn Smythe Trophy as the most valuable player of the playoffs. MacInnis became the first defenceman to lead the league in post-season scoring, and he finished with a 17-game scoring streak, the longest by a defenceman in NHL history.
MacInnis married his wife Jackie shortly after winning the Stanley Cup in 1989, and the couple have four children, Carson, Ryan, Lauren and Riley. MacInnis settled in St. Louis following his retirement, and in 2006 was named the Blues' Vice-President of Hockey Operations. He coaches his children's minor hockey teams, and in 2008–09 coached the St. Louis Junior AAA Blues to a 73–3–2 record and the championship title at the 50th Quebec International Pee-Wee Hockey Tournament. His son Ryan was a member of the Kitchener Rangers, and was drafted by the Arizona Coyotes in the 2014 NHL Entry Draft. His daughter Lauren has committed to play ice hockey at Northeastern University.