A late bloomer who switched from forward to defense in junior hockey, the undrafted Garrison drew notice from NHL teams while at the University of Minnesota-Duluth, even though injuries limited him to 87 games in his three college seasons.

Garrison signed with the Florida Panthers before the 2008-09 season, foregoing his final year of college eligibility. Following a full season in the American Hockey League - there was a one-game call-up his first year - Garrison played 39 games for the Panthers in 2009-10.

By the next season he was a regular on defense, and he broke out in 2011-12, setting a Panthers record for goals by a defenseman with 16 and tying the team mark for power-play goals by a defenseman with nine.

The White Rock, British Columbia native signed a six-year contract with his hometown team, the Vancouver Canucks, in July 2012, but Vancouver traded him to Tampa Bay before the 2014-15 season.

Garrison helped solidify the Lightning defense, settling in a top-four role and becoming a key penalty-killer as Tampa Bay reached the Stanley Cup Final in 2015 and the Eastern Conference Final in 2016.

In Tampa Bay's 2015-16 season-opening victory against the Philadelphia Flyers, Garrison became the first player to score an overtime goal in the new 3-on-3 format. In 2016, he scored the winning goal in overtime of Game 4 of the Second Round of the Stanley Cup Playoffs against the New York Islanders.