Born in 1950 in Kitchener, Ontario, one of eight children in the Sittler family, Darryl first played his way to prominence with the London Knights of the Ontario Hockey Association. Sittler played a determined game and the Leafs made him the eighth pick overall in the 1970 Entry Draft. He saw limited action in his first pro season in 1970-71 and had an unremarkable sophomore year. In 1972-73, he began to establish himself as an offensive star, finishing with 77 points - a total he would better in all but three of his subsequent 12 seasons in the NHL. The Leafs were in a rebuilding phase early in his career and many veterans either retired or were traded. When Dave Keon moved to the World Hockey Association, the 24-year-old Sittler took over the captain's duties, becoming the second-youngest captain in Leafs history after Teeder Kennedy.
Sittler had an incredible year in 1975-76. On February 7, 1976, he produced the greatest offensive game in the history of the National Hockey League, guaranteeing his place in the record books even after Wayne Gretzky had come and gone. Toronto was hosting the Boston Bruins, a team on a seven-game winning streak. The Bruins had recently reacquired Gerry Cheevers, but coach Don Cherry wanted to give the goalie a rest before his upcoming Boston homecoming and started rookie netminder Dave Reece instead. The Leafs beat up the Bruins 11-4, but Sittler was the big story. He had two assists in the first period, three goals and two assists in the second and another hat trick in the third. The total of six goals and four assists set a league record for points in one game that had previously been held by Maurice "Rocket" Richard with eight.
The big night helped Sittler become the first Leaf to reach the 100 mark in scoring in a season, collecting 41 goals and 59 assists. But he wasn't finished. During the playoffs in April against the Philadelphia Flyers, Sittler scored five goals in one game, tying the playoff record. In September, during the Canada Cup in Montreal, Sittler would make headlines again with his scoring ways. This time it wasn't the quantity but the quality and the timeliness that made the impression. In overtime of the second game of the best-of-three finals versus Czechoslovakia, Sittler held onto the puck on a partial breakaway until Czech goalie Vladimir Dzurilla committed himself and an opening presented itself. The goal secured the championship and made Sittler an overnight hero in Canada.
In 1977-78, Sittler registered 117 points and was selected to the league's Second All-Star Team. The Leafs had their best playoff showing in years, making it to the semi-finals. But things began to fall apart, for the franchise and for its captain, in 1979-80 when cantankerous owner Harold Ballard replaced much of his management, bringing in Punch Imlach to run the team.
Sittler was represented by Alan Eagleson, a lawyer and agent who never saw eye to eye with Ballard or Imlach. Relations were strained to the point that Sittler took a pair of scissors to the "C" on his sweater before a game in late 1979 to protest, among other things, the trade of Lanny McDonald to the Colorado Rockies. Ballard then threatened to lock Sittler out before the beginning of the next season. The two men resolved some of their differences and Sittler returned as captain, but it was a tenuous reconciliation. Midway through the 1981-82 season, Sittler went AWOL and demanded a trade. He was depressed and worn out from his battles with management in Toronto. In January he was sent to the Philadelphia Flyers, a one-time nemesis but a team that nonetheless had a great deal of respect for Sittler.
After recovering from the nasty divorce with the Leafs, Sittler had a great season in 1982-83, netting 83 points and a spot in the All-Star Game. He was shocked when Philadelphia traded him to the Detroit Red Wings before the 1984-85 season. Unsure if he wanted to continue and move his family to yet another city, Sittler refused to report for five days. He did end up playing one year with Detroit, though at times he struggled to find a place in the lineup. He retired after the season. Darryl Sittler was inducted into the Hockey Hall of Fame in 1989. Two years later he returned to the Toronto Maple Leafs, this time working in the club's management in marketing and public relations.