He spent his entire NHL career, which lasted from 1977 to 1987, with the Islanders, and was a crucial part of their four consecutive Stanley Cup championships in the early 1980s.

Bossy was the fifth son among ten children,[1] and grew up in a family of Detroit Red Wings fans in the parish of Saint-Alphonse,[2] in the Ahuntsic-Cartierville area of Montreal.

[3] His mother Dorothy was English and French-Canadian, and his father Borden,[1] who maintained a backyard ice rink at their apartment building, was Ukrainian.

[2] When he was 12 years old, Bossy broke a kneecap while competing in long jump at school, later developing chronic knee problems during his hockey career.

[10] Toronto expected him to hold out for more than they wanted to pay, according to Bossy, while the Rangers opted for highly-ranked Lucien DeBlois and Ron Duguay.

[11] Bossy replaced Billy Harris on the Islanders' top line with Bryan Trottier and Clark Gillies, creating a new combination that came to be known as The Trio Grande.

[21] Bossy had boldly told Bill Torrey before the season he would score 50 goals, and wound up with a total of 53,[14] setting a rookie record which stood until broken by Teemu Selanne in 1993.

[29] During the season Bossy represented the NHL All-Stars in the 1979 Challenge Cup against the Soviet Union, scoring against Vladislav Tretiak in the first game of the three-game series.

[40] Coach Al Arbour split up the Trio Grande by shifting Gillies, but while Bossy and Trottier still scored the bulk of the team's goals the remaining lines were ineffectual.

[40] The acquisition of Goring made splitting up the Trio Grande more workable, as Gillies went with him, while Bossy and Trottier were joined on the second line by Bob Bourne, and the Islanders attack became more balanced.

[1] In the 1980–81 season, Bossy and Charlie Simmer of the Kings contended to be the first to score 50 goals in 50 games since Maurice Richard 36 years earlier.

[58] In the opening round of the 1981 Playoffs, Bossy and Trottier tied for the team lead with 10 points each, as the Islanders swept the Maple Leafs.

[63] The Islanders then defeated the Minnesota North Stars in the 1981 Stanley Cup Finals, as Bossy set records for most points (35), and power-play goals (9) and most goals combining regular season and playoffs (85; 68 regular season plus 17 playoff), and the Islanders won their second Stanley Cup.

[67] A late-season knee injury limited Bossy's mobility in the Islanders' Patrick Division semifinal against the Pittsburgh Penguins,[68] although he still managed to score goals in the first two games.

[69] In the Patrick Division final, the Islanders next faced the Rangers, against whom Bossy had scored six goals with nine assists in eight regular season games.

[85] In the Patrick Division semifinal against the Washington Capitals, Bossy scored a hat trick in game 4, as the Islanders won the series with a 6–3 victory.

[95] On January 15, Bossy scored his 400th career regular season goal, the fastest to hit that milestone, doing so in his 506th game, a 4–2 win against the Rangers.

[104][105] Bossy started the 1984–85 NHL season strong, tying his own team record by scoring in ten consecutive games, and by early November was leading the league with 33 points.

[108][109] After Trottier returned, he took his usual place alongside Bossy, joined with Greg Gilbert,[108] but the Bossy-Tonelli-Sutter combination would be resurrected later in the season when the team needed a boost.

On January 2, 1986, Bossy became the fastest player to reach 500 goals in NHL history, scoring twice in his 647th game, a 7–5 victory against the Boston Bruins.

[123] Bossy's four-goal game against Calgary on March 11 included his 50th of the year, making this the record-setting ninth straight season in which he had scored at least 50 goals.

[24] In the 1986 NHL All-Star Game, Bossy assisted on Bryan Trottier's overtime game-winning goal in a 4–3 Wales Conference victory.

[128] At the beginning of training camp Bossy experienced back pain, and after playing two uncomfortable games in which he did not score, he was ordered to rest for 10 days.

[130] By Christmas, Bossy had 22 goals but was playing through pain and was not at his usual level, and was undergoing chiropractic treatments and considering taking time off in February.

[133] It was believed that he was putting undue strain on his back by skating in a manner to take pressure off his right knee, which had required surgery when he was a child;[134] Bossy had broken the kneecap when he was twelve.

[137] However, by late March it was apparent to Bossy that he would not be reaching the milestone, as the pain increased, and he additionally found himself the target of hits that exploited his condition.

[147] Doctors eventually concluded that he had two discs in his lower back that were damaged and could not be repaired by surgery, leading Bossy to sit out the 1987–88 season in favour of therapy.

In Stan Fischler's The All-New Hockey's 100, Bossy says, "About 90 percent of the time I don't aim: I just try to get my shot away as quick as possible as a surprise element.

"I called the Canadiens at least two or three times [in the mid-1990s] because I thought I could help the organization in some way, not necessarily as a coach but in some role that could be developed", Bossy told Sports Illustrated in 2005.

[180] Bossy met his future wife Lucie Creamer when he was 14, and she was working the snack bar at a rink where he was playing; they were married July 23, 1977.