Doug Gilmour was born June 25, 1963, in Kingston, Ontario. He is the younger son of Don and Dolly Gilmour, and has an elder brother, David. Don was a correctional officer who worked at the Kingston Penitentiary for over three decades. He also coached youth baseball and hockey teams in the city. As a youth, Doug looked up to David, who was a professional hockey player drafted by the Vancouver Canucks but never played in the National Hockey League (NHL). The younger Gilmour played in the 1976 Quebec International Pee-Wee Hockey Tournament with a minor ice hockey team from Kingston.

The Cornwall Royals of the major junior Quebec Major Junior Hockey League (QMJHL) drafted Gilmour from Belleville, and he joined the team for the 1980–81 season. The Royals were the defending Memorial Cup champions, and Gilmour was not expected to play a significant role with the team. The Royals started him off as an offensive defenceman, but moved him to forward permanently. As national champions, the Royals represented Canada at the 1981 World Junior Ice Hockey Championships. Gilmour appeared in all five tournament games, though he scored no points, as the team struggled to a seventh-place finish in the eight team tournament. In the QMJHL, Gilmour’s season was interrupted by a broken collarbone. He finished the year with 35 points in 51 games. The Royals won the QMJHL championship and earned a berth in the 1981 Memorial Cup. Gilmour recorded seven points in five games at the tournament. Cornwall faced the Ontario Hockey League (OHL)’s Kitchener Rangers in the championship game. Cornwall won 5–2 to repeat as national champions; Gilmour scored the winning goal midway through the second period.

Though eligible for the 1981 NHL Entry Draft, Gilmour went unselected and returned to Cornwall, who had shifted to the OHL for the 1981–82 season. 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. NHL teams continued to dismiss Gilmour due to his size, but the St. Louis Blues gambled on him in the 1982 NHL Entry Draft by selecting him with their seventh round pick, 134th overall. The Blues returned him to Cornwall for the 1982–83 season where he led the OHL in goals (70), assists (107) and points (177). Gilmour won the Eddie Powers Memorial Trophy as the leading scorer, was named a league all-star, and was named recipient of the Red Tilson Trophy as the OHL’s most outstanding player. His season total of 177 points is the third highest in OHL history, behind Bobby Smith (192) and Wayne Gretzky (182). Gilmour had a 55-game point streak that lasted from October 19, 1982, until February 27, 1983, and which remains an OHL record.

Despite his performance in Cornwall, the Blues did not make signing Gilmour a priority. Unsure if a contract offer would materialize, Gilmour made plans to play in Düsseldorf, West Germany, and had already traveled to Europe when the Blues finally offered him a deal in mid-August 1983. St. Louis coach Jacques Demers believed Gilmour had the potential to be a defensive specialist at forward. He began the 1983–84 season in St. Louis and made his NHL debut on October 4, 1983, against the Pittsburgh Penguins. Gilmour scored his first goal on November 1, in his 12th game, against Eddie Mio of the Detroit Red Wings. He finished the season with 25 goals and 53 points. Teammate Brian Sutter began calling Gilmour “Charlie”, after Charles Manson, in reference to both his “mean” style of play and an apparent resemblance to the serial killer; it morphed into “Killer”, a nickname Gilmour retained throughout his career.

Gilmour’s offensive performances were consistent in his following two seasons. He recorded 57 points in 1984–85 and 53 points in 1985–86. Defensively, Demers matched Gilmour up at centre against the opposition’s best players and he played an agitator role. Over time, he gained confidence in his ability to both defend against the opposition and play an offensive role. 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. 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 Final. The Blues were eliminated in the Campbell Conference Final by the Calgary Flames. His offensive breakout continuing into the 1986–87 season, Gilmour led the Blues and finished fifth overall in NHL scoring with 105 points; his 42 goals was the highest single-season total of his career. His performance in the NHL season earned Gilmour an invitation to join Team Canada at the 1987 Canada Cup. He had two goals in the tournament as Canada won the championship.

Gilmour became embroiled in a legal conflict. He was sued in August 1988 by the parents of a 14-year-old girl who alleged that Gilmour had sexually assaulted their daughter. His wife Robyne, the Blues organization and the team’s president Jack Quinn were also named in the $1 million lawsuit as it was alleged that they “knew or should have known” about the alleged abuse. The Blues were also accused of pretending to negotiate a payment while attempting to trade Gilmour without informing the other team of the allegations. One week later, on September 6, the Blues traded Gilmour to the Flames in a multi-player deal. Gilmour, Mark Hunter, Steve Bozek and Michael Dark were sent to Calgary in exchange for Mike Bullard, Craig Coxe and Tim Corkery. Gilmour expressed disappointment at leaving the Blues, but stated that “from what has happened the past week, on our part and on the St. Louis Blues’ part, it was our best solution.”

An off-season salary dispute with Flames’ general manager Doug Risebrough carried into the 1991–92 season. Gilmour, who was playing the option year of his contract at a salary of US$450,000 was unable to reach a deal with the team on an extension. The dispute went to arbitration where the Flames offered a raise to $550,000 while he asked for $1.2 million and was expecting a settlement worth around $800,000. The arbitrator’s decision, made in December 1991, amounted to $750,000 per season for two years, but left Gilmour angry and bitter. He alleged that executives with the team and league had tampered with the process – the arbitrator attended a Flames game with team management on the night before the hearing, while NHL President John Ziegler sent a letter to the arbitrators. Gilmour, who remained active with the Flames throughout the process, had scored 38 points in 38 games. Following the decision, he requested a trade out of Calgary and threatened legal action. 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. He later called the choice to walk away from the team to be one of the toughest decisions he had ever made.

In his first full season with the Maple Leafs, 1992–93, Gilmour had the finest season of his career. He broke Toronto franchise records for assists (95) and points (127), and on February 13, 1993, tied Babe Pratt’s franchise record by assisting on six goals in one game. Gilmour finished seventh overall in NHL scoring, but was also subject to a controversial suspension during the year. The league suspended Gilmour for eight practice days – but no games – after he broke Tomas Sandström’s forearm with a slash. The Maple Leafs finished the season with the eighth-best record in the NHL, and posted their first winning season since 1978–79.

In the 1993 Stanley Cup Playoffs, Gilmour broke the team scoring record by scoring 35 points as Toronto reached the Campbell Conference Final. The sixth game of the series, against the Los Angeles Kings, ended in controversy. Toronto led the series three games to two and one additional victory would have put the Maple Leafs into the Stanley Cup Final for the first time since 1967. 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. Instead, Gretzky remained on the ice and scored the game-winning goal seconds later. Gretzky then led Los Angeles to a game seven victory that eliminated Toronto from the playoffs. 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.

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. The Maple Leafs agreed to renegotiate Gilmour’s contract following the season; the two sides agreed to a five-year, $15 million contract early in the 1993–94 season that included endorsement rights and was expected to allow Gilmour to complete his career in Toronto.

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. The 1994–95 season was delayed by a labour dispute. The stoppage prompted several players to sign temporarily with European teams. Gilmour signed in Switzerland and joined the Rapperswil-Jona Lakers in November 1994. He appeared in nine games with the National League A team and scored two goals to go along with 13 assists before returning to Canada. He also attempted to join Wayne Gretzky’s exhibition tour of Europe when able. Gilmour returned to the Maple Leafs when the NHL’s dispute was resolved; in 44 games with Toronto, he had 10 goals and 23 assists.

Gilmour reached a career milestone during the 1995–96 season as he scored his 1,000th career point on December 23, 1995, in a 6–1 victory over Edmonton.

With the Leafs struggling once again, Cliff Fletcher traded Gilmour and defenseman Dave Ellett to the New Jersey Devils in 1997 for centerman Steve Sullivan, prospect Alyn McCauley and defenseman Jason Smith. The Devils during Gilmour’s tenure would then suffer early playoff exits.

Gilmour’s Blackhawks played against the Toronto Maple Leafs on February 13, 1999 as the last game in historic Maple Leaf Gardens was played. Gilmour scored in the game and was given a standing ovation by the Toronto fans during the Gardens’ closing ceremonies. Gilmour suffered a back injury (herniated disk) late in the season and had to undergo season-ending surgery.

Gilmour signed as a free agent in 2001 with the Montreal Canadiens. The Canadiens would make the playoffs that season, eventually being beaten by the Carolina Hurricanes.

The Canadiens traded Gilmour to the Maple Leafs for a sixth round draft pick at the 2003 NHL trade deadline. Gilmour’s first game with the Leafs turned out to be his last as he and the Calgary Flames Dave Lowry collided inadvertently during Gilmour’s second shift, with Gilmour tearing his ACL and missing the remainder of the season. Gilmour officially announced his retirement on September 8, 2003 after John Ferguson, Jr. made a public announcement that the Maple Leafs would not re-sign the veteran center.

On September 15, 2006, the Toronto Maple Leafs announced that Gilmour would become their player development advisor. Gilmour held that position with the Leafs until August 7, 2008, when the Maple Leafs announced that Gilmour would join the Toronto Marlies, the Leafs American Hockey League affiliate, as an assistant coach under Marlies head coach Greg Gilbert. 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.

Gilmour was named head coach of the Kingston Frontenacs on November 17, 2008, taking over a rebuilding club that had a 5–13–5 record under Larry Mavety, who had coached Gilmour with the Belleville Bulls when the Bulls were still in the OPJHL. Gilmour finished out the season with Kingston with a 13–27–5 record in their last 45 games and the team failed to make the playoffs.

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. Gilmour became the seventeenth player to be honoured in such a way by the Maple Leafs. He was inducted into the Hockey Hall of Fame in 2011. On October 15, 2016, Gilmour’s number 93 was retired by the Maple Leafs, along with all other honoured numbers also being retired.

He stepped down as general manager and became the president of the Frontenacs in 2017. In 2019, he left the team to become a community representative for the Maple Leafs.