Drafted by the New York Islanders in 1974, Trottier played his first fifteen seasons in New York.

He was one of the core players of the Islanders' early 1980s dynasty wininng four Stanley Cups with them in 1980, 1981, 1982, and 1983. His best season was 1978-79 when he had 134 points, top in the NHL that season. In the same season, he led the NHL in assists with 87, something he did the year before as well with 77 assists.

After fifteen years with New York he was picked up as a free agent by the Pittsburgh Penguins where he played his remaining three seasons winning two more cups in 1991 and 1992. He retired in 1994.

In the late Seventies and early Eighties, despite Wayne Gretzky's dominance, Trottier was still universally regarded as the game's best all-around player, combining potent offense, rock-solid defense, and expert play on special teams. 

In 1997, he was inducted into the Hockey Hall of Fame in his first year of eligibility. In 2001, Trottier was an Assistant Coach for the Stanley Cup winning Colorado Avalanche.  On June 1, 2006, he was named the Islanders' Executive Director of Player Development.