Upon retiring at the end of the 1983–84 season with 358 goals and 852 assists for a total of 1,210 points in 1,144 career games, he immediately became general manager of the Flyers.

His time as an NHL general manager had its share of controversy, perhaps none greater than the rift between him and star player Eric Lindros during the late 1990s and early 2000s.

[8] Born in the small northern Manitoban mining town of Flin Flon,[9] Clarke began playing organized hockey when he was eight years old.

[9] Bombers coach Pat Ginnell took Clarke to the Mayo Clinic in Minnesota following the 1967–68 season and the doctors concluded that as long as he took care of himself he could play professionally.

[10] Even with such assurances Clarke fell to the second round of the 1969 NHL Amateur Draft and was finally selected by the Philadelphia Flyers 17th overall.

After Gerry Melnyk, a scout and administrative assistant with the Flyers, tried to convince general manager Bud Poile to draft Clarke with their first-round pick and failed[12] — Poile drafted Bob Currier instead, a player who retired five years later and, ironically, never played a game in the NHL — Melnyk called a diabetes specialist in Philadelphia who said Clarke would be fine if he looked after his health.

[15] Clarke played the entire 76-game schedule his rookie season and recorded 46 points (15 goals, 31 assists) while earning a trip to the NHL All-Star Game.

[16] He was also named NHL Rookie of the Year by The Sporting News,[17] and finished fourth in voting for the Calder Memorial Trophy.

[16] A few months following his strong play during the Summit Series for Team Canada, Clarke was named the Flyers' captain at age 23, the youngest to ever assume that role in NHL history at the time.

Facing the Minnesota North Stars in the first round, the Flyers and Clarke received a scare, as he was hit in the eye with a stick which broke his contact lens and was rushed to the hospital.

[12] After removing parts of his broken contact from under the eye, Clarke returned to the lineup the next game despite having suffered a scratched cornea,[12] and the Flyers won their first playoff series.

[6] Clarke played a key role in the Finals in countering Bruins' star players, winning 48 of the 66 face-offs against Phil Esposito, and neutralizing Bobby Orr by chasing him down.

The Stanley Cup winning goal in game six was scored after a fight between Clarke and Orr that sent both players to the penalty box.

However, Montreal coach Scotty Bowman's strategy successfully prevented Clarke's line from scoring and the Flyers were swept in four straight games.

[12] In order to become an assistant, he had to give up the captaincy due to NHL rules,[12] so Mel Bridgman was named the 4th captain in Flyers history.

[12] 31 seconds into the third period Clarke beat Bruins goalie Marco Baron for his 19th goal of the season[24] and his 1000th career point.

He played a major role in defeating the Soviet Union during the Summit Series in 1972, captained the Canadian team to gold at the 1976 Canada Cup, and won a bronze medal at the 1982 World Championships.

Coming off his third NHL season, Clarke was the last player Team Canada selected to play in the Summit Series.

[31] When asked about the slash years later, Clarke said, "If I hadn't learned to lay on a two-hander once in a while, I'd never have left Flin Flon.

"[31] John Ferguson, Sr., an assistant coach with Team Canada in 1972, said, "I called Clarke over to the bench, looked over at Kharlamov and said, 'I think he needs a tap on the ankle.'

A few of Clarke's choices were the source of some consternation, in particular omitting Mark Messier in favour of surprise selection Rob Zamuner[35] and choosing 24-year-old Eric Lindros as the team's captain over the likes of Wayne Gretzky, Ray Bourque, and Steve Yzerman.

[36] Ranked number one going into the tournament, Team Canada played strongly until being stymied by Czech goaltender Dominik Hašek in the semifinals, losing in a shootout.

Following his retirement, Clarke's first stint as Flyers general manager lasted six seasons and included two trips to the Stanley Cup Finals in 1985 and 1987.

During his second tenure as general manager of the Flyers, the team made the playoffs 11 seasons in a row but reached the Finals once (1997).

By contrast, the New Jersey Devils, their Atlantic Division rivals, were stable in net with Martin Brodeur and beat the Flyers in the Conference Finals en route to Stanley Cups in 1995 and 2000.

Some suggested Clarke's handling of Neilson, who took a medical leave in February 2000 to undergo cancer treatment and was replaced by Craig Ramsay, was disrespectful.

"[42] Ramsay guided the team to the Eastern Conference Finals in 2000, but he was fired after a subpar start in 2000–01, being replaced by Clarke's former linemate Bill Barber.

[40] Following the 2004–05 NHL lockout, Clarke signed 6'5" defencemen Derian Hatcher and Mike Rathje to four-year and five-year contracts respectively.

[44] Lindros' parents criticized team trainer John Worley and claimed Clarke tried to kill their son by trying to put him on a plane back to Philadelphia, which would have been fatal given his condition.

Lindros pushed for a trade to Toronto but that move fell apart at the last minute when Clarke and Leafs manager Pat Quinn could not agree on terms.