A two-time All-Star, he was a member of Calgary's 1989 Stanley Cup championship team and won the Frank J. Selke Trophy as the NHL's best defensive forward in 1992–93.

Gilmour returned to the OHL following his playing career as he joined the Kingston Frontenacs as head coach in 2008 and was promoted to general manager in 2011.

Instead, he was offered a spot with the Junior A Belleville Bulls, with whom he began as a defenceman but shifted to left wing during the playoffs due to injuries.

Cornwall won 5–2 to repeat as national champions; Gilmour scored the winning goal midway through the second period.

[2] He played a more significant role with the Royals and led the team offensively; Gilmour's 119 points in 67 games was sixth best in the league.

[5] Gilmour established a role as a top offensive scorer for the Blues in the 1986 Stanley Cup playoffs as he recorded 21 points in 19 games.

[22] He tied with teammate Bernie Federko for the league lead in playoff scoring, despite the fact that the Blues failed to reach the Stanley Cup Finals.

[23] His offensive breakout continuing into the 1986–87 season, Gilmour led the Blues and finished fifth overall in NHL scoring with 105 points;[24] his 42 goals was the highest single-season total of his career.

Two seconds after Ken Linseman scored for Boston, Gilmour replied for St. Louis as the pair combined to set a record for the fastest two goals in league history.

Gilmour, Mark Hunter, Steve Bozek and Michael Dark were sent to Calgary in exchange for Mike Bullard, Craig Coxe, and Tim Corkery.

"[28][29] Gilmour's legal situation progressed throughout the early part of the 1988–89 NHL season as he began his career with the Flames: He and his wife countersued his accusers for slander and libel in October,[30] and a grand jury was convened to investigate whether criminal charges were warranted.

[33] Gilmour played a pivotal role in the Flames' run to the 1989 Stanley Cup Finals; he was particularly effective in Calgary's second round series against the Los Angeles Kings where he scored or assisted on key goals in three of the four games while playing an effective role in preventing the Kings' star Wayne Gretzky from establishing his own offensive game.

[9] In the sixth game of the final, against the Montreal Canadiens, he scored two goals – including the championship winning tally – in a 4–2 victory that clinched the Flames first Stanley Cup.

[24] He also became embroiled in a physical melee with Los Angeles Kings assistant coach Tom Webster late in the season.

Gilmour led the Flames to a 3–2 overtime victory over the Montreal Canadiens with a goal and an assist on New Year's Eve then walked out on the club on January 1, 1992.

[41] The following day, Calgary dealt Gilmour to the Toronto Maple Leafs as part of a ten player swap, the largest trade in NHL history.

Calgary sent Gilmour, Jamie Macoun, Ric Nattress, Kent Manderville and Rick Wamsley to Toronto in exchange for Gary Leeman, Craig Berube, Michel Petit, Alexander Godynyuk and Jeff Reese.

[51] Toronto led the series three games to two and one additional victory would have put the Maple Leafs into the Stanley Cup Finals for the first time since 1967.

[52] In the first minute of overtime with the score tied 4–4, Gilmour was cut on his chin for eight stitches after he was struck by Wayne Gretzky's stick.

League rules of the time mandated that player who caused an injury via a high-sticking infraction be assessed a five-minute penalty, however referee Kerry Fraser made no call on the play, even after conferring with his linesmen.

[52] Toronto fans remain bitter about the non-call two decades after the fact, while Fraser – who explained he did not have a clear view of the play – admitted it was the worst mistake he made in over 2,100 games as an NHL referee.

[51] Individually, Gilmour earned several accolades for his season: He played in the 1993 All-Star Game (his first of two consecutive appearances), was named recipient of the Frank J. Selke Trophy as the NHL's top defensive forward, and finished second to Mario Lemieux in voting for the Hart Memorial Trophy as the league's most valuable player.

[56] He finished fourth in post-season scoring with 28 points as the Maple Leafs again reached the Western Conference Final before losing to the Vancouver Canucks.

[20][58] The Maple Leafs named Gilmour the 15th captain in franchise history on August 18, 1994, as he succeeded Wendel Clark, who was traded to the Quebec Nordiques in the off-season.

In the spring of 2000, with the Blackhawks once again floundering among the bottom of the NHL, Gilmour was traded to the Buffalo Sabres along with left winger J.P. Dumont for forward Michal Grošek.

Following his first year with Montreal, which saw the centre record 41 points, Gilmour resigned with the Canadiens to a one-year contract with an option for the 2003–04 season on August 9, 2002.

On January 31, 2009, Gilmour's number 93 was honoured by the Toronto Maple Leafs as it was raised to the rafters at Air Canada Centre.

[69] Gilmour held that position for only a few months before leaving the Maple Leafs' organization to become the head coach of the Kingston Frontenacs of the OHL in November 2008.

At the conclusion of the season, Gilmour left the Frontenacs' head coaching position to become the team's general manager, replacing good friend Larry Mavety, who became an advisor to the club.

Kingston saw some improvement during the 2012–13 season, as the team finished with a 27–35–6 record, earning 60 points, good for seventh place in the conference, and a playoff spot.