Within days after the Summit Series, he signed a five-year deal to return to the Bruins as their general manager, His 28-year tenure almost equalled the 30-year reign (1924–54) of
Art Ross, the team's founding manager. Sinden, who had added the title of club president in December 1988, remained as the chief executive of the Bruins until the summer of 2006 when he retired to a consulting role. As general manager of the Bruins, Sinden presided over the team's long years of consistent success, setting the North American major professional record for most consecutive seasons in the playoffs with 29, which included making the finals five times (1974, 1977, 1978, 1988, 1990 — losing the finals each time) and two regular-season first-place finishes (1983, 1990). With the Bruins, he became the first NHL general manager to reach 1,000 wins, setting the milestone on October 17, 1995. He finished with a impressive all time record of 1170-763-301, with a .591 winning percentage. He was named executive of the year by
Sporting News twice in 1977 and 1990. Notwithstanding this longstanding success, he was the subject of controversies ranging from video replays to salary arbitration and was under frequent fire from Bruin fans. In the
1996–97 season, the NHL fined him $5,000
USD for verbal abuse of a video-replay official who had disallowed a goal in the second period of a game between the Bruins and the
Ottawa Senators. He also refused to honor a salary-arbitration award and let
Dmitri Khristich, a 29-goal scorer, leave the team without compensation. He had been highly critical of Khristich's performance in the playoffs and was angered when an arbitrator awarded him a salary of $2.8 million. He was inducted into the Canada sports Hall of Fame in 2005. Sinden is currently the Bruins'
Senior Advisor to the Owner, as well as a former member of the selection committee for the
Hockey Hall of Fame. He is also a "Hockey GM & Scouting" instructor for the online sports-career training school
Sports Management Worldwide, founded and run by
Dr. Lynn Lashbrook. In 2011, his name was inscribed on the Stanley Cup for a second time, 41 years after his first Stanley Cup title as a coach. Sinden has served as an integral member of the Bruins organization for over 60 years. He still regularly appears at alumni events, Bruins ceremonies, and charity causes. In 2024, he was honored during the teams centennial festivities as a team legend. ==Awards and achievements==