Reinhart, 25, was a restricted free agent. Florida got him from the Sabres last month for a first-round draft pick and goalie prospect Devon Levi.
Reinhart's contract carries the highest cap hit of any forward on the Panthers. That includes point-per-game producers Aleksander Barkov and Jonathan Huberdeau. The 25-year-old Barkov has another season on his deal at $5.9 million. And Huberdeau, 28, has two years left at the same cap hit.
Those two will be due big raises, but Reinhart was due for one as well. He played on a one-year, $5.2 million deal last season with the struggling Sabres. On a team filled with injuries and dysfunction, he scored 25 goals and added 15 assists in 54 games. He has scored more than 20 goals in the last four seasons and five of the last six.
Reinhart was the second overall pick in the 2014 NHL draft behind current Panthers defenseman Aaron Ekblad.
"Sam is a gifted and versatile talent that will play a key role for our team in the coming seasons," Panthers general manager Bill Zito said in a statement. "One of several players to commit to our organization with a multi-year contract this offseason, we are excited to see how these players come together and continue to build a foundation for success in South Florida."
The Panthers were second in the Central Division last season, behind the Hurricanes and ahead of the Lightning. They lost in six games to eventual champion Tampa Bay in the first round of the playoffs.