Gallant previously played eleven seasons in the NHL, primarily for the Detroit Red Wings, but also including a short stint with the Tampa Bay Lightning.

[2][3] Gallant stated that when he first got to the NHL, a lot of the guys also called him "Spuddy" because of Prince Edward Island's reputation as the potato capital of Canada.

[4] After his first junior season in 1981, Gallant finished as runner-up to Claude Verret in voting for 1980–81 Michel Bergeron Trophy as QMJHL offensive rookie of the year.

[6] Gallant split the 1984–85 season between the AHL and NHL, making his Detroit Red Wings debut against the New York Islanders on January 22, 1985.

[7] In his first game, he scored against Islanders' goaltender Billy Smith in the second period of a 5–4 Detroit victory that snapped a 12-game Red Wings' winless streak.

In March 1991, he was forced to undergo surgery to remove a bone spur from his back, causing him to miss the rest of the regular season and the playoffs.

He provided his usual physical presence and finished with a +16 and +20 plus/minus rating; however, was unable to duplicate his scoring prowess and the Wings did not offer him a contract to return.

Playing alongside Red Wings teammate Steve Yzerman, Gallant scored two goals and had three assists in eight games as the Canadians won the silver medal.

[10] Despite his smaller stature (5 ft 10 in, 180 lbs), Gallant played the role of power forward during his time with the Red Wings – similar to NHL contemporary Kevin Dineen.

Playing on the Red Wings top line alongside star Steve Yzerman and either Bob Probert or Paul MacLean,[11] he was among the team leaders in both goals and penalty minutes.

Gallant's 1988–89 line of 39 goals, 54 assists, and 230 penalty minutes was the first of its kind in NHL history, only matched later by Kevin Stevens in 1991–92 and Rick Tocchet in 1992–93.

[12] Detroit's coach at the time, Jacques Demers, said he thought Gallant's penchant for fighting was the only thing holding him back from a 50-goal season.

"[13] Gallant began his coaching career in 1995–96 with his hometown Summerside Capitals of the Maritime Junior Hockey League, leading the team to the Royal Bank Cup in 1997.

[14][15] He spent the 1999–2000 season serving as an assistant for the Louisville Panthers of the AHL under head coach Joe Paterson, a former teammate of Gallant's in Detroit.

[16] Gallant then served as an assistant for the Columbus Blue Jackets of the NHL from 2001 to 2004 under head coaches Dave King and Doug MacLean.

MacLean, who was also serving as the Blue Jackets general manager, resigned as head coach on January 1, 2004, and named Gallant as his successor.

[18] In 2007, Gallant was named by Team Canada general manager Steve Yzerman as one of the two assistant coaches for the 2007 Men's World Ice Hockey Championships.

During his three seasons with Saint John, he compiled a 159-34-9 record and led the Sea Dogs to three first-place finishes, three league final appearances, two QMJHL championships (2011 and 2012), and one Memorial Cup (2011).

[3][20] On June 21, 2014, he was named head coach of the NHL's Florida Panthers by then-executive vice president and general manager, Dale Tallon.

[23] Gallant led the Golden Knights to one of the most successful debut seasons for an expansion team in North American major professional sports history.