Cournoyer's professional hockey career began in 1961 with the Montreal Junior Canadiens of the Ontario Hockey Association. By the time he was 18 years old, his legs had become so muscular that he required specially tailored pants. Cournoyer made his NHL debut in 1963 with the Montreal Canadiens and earned a full-time spot with the club in 1964 after just seven games with the American Hockey League's Quebec Aces. Cournoyer was initially regarded by Canadiens head coachToe Blake as a defensive liability and undeserving of a regular shift, though he was still frequently used on the power play. That changed after Blake's departure following the 1968 Stanley Cup Championship, when incoming coach Claude Ruel granted Cournoyer a full-time shift. Cournoyer went on to have his first 40-goal season in 1968–69 and was named to the NHL's Second All-Star Team. Cournoyer scored a career high 47 goals in the 1971–72 season. In 1973, he had his best postseason ever, scoring 15 goals and tallying 10 assists in 17 games, earning the Conn Smythe Trophy following the Canadiens' defeat of the Chicago Black Hawks in the Stanley Cup Finals. Cournoyer was named captain of the Canadiens in 1975 following the retirement of Henri Richard, pushing him to play harder in his new leadership role. Cournoyer would become only one of the Habs' two captains to win Stanley Cups throughout his entire tenure as captain, the other one being Maurice Richard, Henri's older brother. The speedy Cournoyer's ability to stay true to his form in his older age was a favourite topic of discussion of the Montreal fans and hockey media, however, and he did slow down due to a disc in his back that was pressing on a nerve and causing him great pain. Cournoyer eventually had to have surgery on his back and missed the entire 1977 postseason. Cournoyer returned for the 1978 season and played in 68 games, scoring 24 goals and collecting 29 assists to match his previous season's total of 53 points, though it was evident his back still bothered him. He managed to perform in the playoffs again, however, with seven goals and four assists in 15 games en route to Montreal's third consecutive Cup. However, he was forced to retire following the 1979 season after playing in just fifteen games. When he retired, he only trailed Maurice Richard, and Jean Beliveau on the Canadiens' all-time scoring list. Cournoyer won a total of 10 Stanley Cups as player, second only to Henri Richard's 11. The Cournoyer legacy includes many Top 10 Canadien records - 7th in total games played, 4th in goals scored, 7th in assists and 6th in total points scored. Cournoyer played for Canada in the 1972 Summit Series, scoring three goals, and is part of the famous picture wherein Paul Henderson jumps into his arms after scoring the game winner. Cournoyer coached the Montreal Roadrunners during the 1994–95 season and was an assistant coach to the Canadiens during the 1996–97 season. He currently serves as an official ambassador to the Montreal Canadiens.