Nicknamed "Trots," he was drafted by the New York Islanders in 1974 where he played his first fifteen seasons. He won the Calder Trophy as the league's Rookie of the year in 1976. Trottier was one of the core players of the Islanders early 1980s dynasty wininng four Stanley Cups with them in 1980, 1981, 1982, and 1983, earning the Conn Smythe trophy as playoff MVP in 1980. His best season was 1978-79 when he had 134 points, top in the NHL that season, garnering the Hart Trophy as league MVP. In the same season, he led the NHL in assists with 87, something he did the year before as well with 77 assists.

Despite Wayne Gretzky's dominance, Trottier was still universally regarded as the game's best all-around player in the early 1980's combining potent offense, rock-solid defense, and expert play on special teams. Unlike other prominent centers of his generation, however, such as Mark Messier and Steve Yzerman, longevity was not his hallmark. Following his 13th season, Trottier's skills seemed to deteriorate precipitously, decreasing from 82 points in 1988 to 45 points just one year later, and 24 points in 1990.

Undaunted by heavy criticism from fellow Canadians, Trottier chose to play for Team USA in the 1984 Canada Cup tournament, after playing for Team Canada in 1981, because he wanted to pay back the country in which he lived and because his wife was American. He was able to obtain the necessary U.S. citizenship in July 1984 because he had Métis ancestry on his father's side (Cree/Chippewa). His North American Indian Card (which he qualified for because his grandmother was a Chippewa) entitled him to citizenship in both the U.S. and Canada, as well as a U.S. passport, which was all he needed for tournament eligibility.

After fifteen years with New York, when he was released by the Islanders, he ranked second in club history in goals, and first in assists and points. He was picked up as a free agent by the Pittsburgh Penguins, winning the Stanley Cup for the fifth and sixth times, in 1991 and `92. He then briefly retired, returning to the Isles in a front office capacity, but finacial troubles, stemming from bad investments, forced Trots to return to the ice for the 1993-94 season. He retired again following a disappointing final season where he scored only 4 goals in 41 games. At the time of his retirement, His point total ranked 6th in NHL history. Trottier was inducted into the Hockey Hall of Fame in his first year of eligibility in 1997.

Trottier again became a topic of controversy after many of his Islander teammates, including linemates Mike Bossy and Clark Gillies were honored by the Islander organization by having their numbers retired. Trottier, still reeling from his financial difficulties, wanted significant financial compensation for his appearance to retire his number 19, delaying the ceremonies for years. His number was finally raised to the rafters on October 20, 2001.

After serving as an assistant coach in Pittsburgh until 1997, he took a similar position with the Colorado Avalanche, where he garnered his 7th career Stanley Cup ring in 2001. He was named as head coach of the New York Rangers in 2002, much to the ire of Islander fans. However, his stint there was short and dismal. In addition to receiving criticism from Isles fans who labeled him a traitor, he drew the rage of Ranger fans as well, who felt he misused his offensively gifted players such as Eric Lindros and Pavel Bure by having them play a neutral-zone trap ( a defensive tactic used to slow down the opponent, but also limiting the user's offensive chances). To the relief of Islander and Ranger fans alike, Trottier was fired after just half a season with New York.

On March 4, 2006, the New York Islanders celebrated the 25th anniversary of their first Stanley Cup championship (actually 26th, but the 2004-2005 season was cancelled due to the NHL lockout). Trottier, apparently forgiven for his stint with the rival Rangers, was given one of the largest ovations of the evening, and was perhaps the most boistrous. He gave a familiar salute to the fans who lined up to watch a pregame "Walk of Champions" entering the building, raising both hands high above his head, reminisant of his days playing on the Island where he would do the same to the fans cheering him on. It had been speculated that with Islander management looking for both a new GM and coaching staff, that "Trots" may soon find himself back home with his original organization. On June 1st, 2006, Trottier finally returned to the Islanders', as Executive Director of Player Personnel.