The deal is worth $7.875 million per season.
"Victor has matured into one of the top defensemen in the NHL and coming off the recent re-signing of our captain, Steven Stamkos, we've secured another extremely important member of our team," general manager Steve Yzerman said in a statement. "I'm very appreciative of both Victor and [agent] Peter Wallen's efforts to reach an agreement with us at this time."
Hedman tweeted about the extension Friday.
Couldn't be more excited to stay in Tampa for another 8 years! Let's do this..
— Victor Hedman (@heds77) July 1, 2016
Hedman had 10 goals and 37 assists for the Lightning last season, his seventh in the NHL. The 25-year-old has 49 goals and 180 assists in 470 career NHL games.
The Lightning drafted Hedman with the No. 2 overall pick in 2009.