Last season, Gallant became one of four coaches to guide the Panthers to the Stanley Cup Playoffs, joining Kevin Dineen, Terry Murray and Doug MacLean. Florida lost to the New York Islanders in six games in the first round of 2016 playoffs.
"Today is a hard day," Panthers president Dale Tallon said. "Gerard and Mike are good men and talented hockey coaches. We thank them for their contributions in the community, for their work developing our young players and in helping to turn around the culture."
Gallant was 96-65-25 with the Panthers. He was hired on June 21, 2014 and signed a two-year contract through the 2018-19 season last January while in the midst of a franchise-record 12-game winning streak.
In his first season in 2014-15, Gallant guided the Panthers to a 38-29-15 record and 91 points, a 25-point improvement over the previous season.
Gallant's first head-coaching tenure also ended in the middle of a season; after taking over as coach of the Columbus Blue Jackets midway through the 2003-04 season, Gallant was replaced after 15 games in 2006-07. The Blue Jackets were 56-76-10 with Gallant as coach.
This marks the sixth time in the Panthers' 23-year history they have made an in-season coaching change. It previously happened in 2013-14 when Peter Horachek replaced Dineen after 16 games.