The deal is for a total of $34.8 million -- an average of $5.8 million per season -- and also includes a full no-trade clause for the first four seasons and he can submit a partial list for the final two, sources told ESPN.com.
Callahan will receive $6 million next season, $6.4 million in 2015-16, $6.5 million in 2016-18 and $4.7 million in the final two seasons of the deal.
Callahan was a pending UFA and other teams were allowed to begin talking to him as of 12:01 a.m. ET Wednesday and other teams did reach out.
"I couldn't be happier to be part of the Tampa Bay Lightning organization for the next six years and I am excited for this new chapter of my career," Callahan said in a release. "Tampa Bay has been a great place to live and play from the day I got there. As soon as the season ended I knew it was a place I wanted to be."
Talks had heated up between Callahan's camp and the Lightning late Tuesday night.
"He's proven to be a fierce competitor and outstanding leader who fits very well with our team," Lightning vice president and general manager Steve Yzerman said in a release.
Callahan, an eight-year veteran who has spent most of career with the New York Rangers, scored 17 goals and had 19 assists last season. The Lightning acquired Callahan from the Rangers in March as part of the Martin St. Louis deal.
Since Callahan has re-signed with the Lightning, the Rangers will receive a 2015 second-round pick from Tampa Bay, per stipulations of that deal. Tampa Bay will get a 2015 seventh-round pick in return.
Callahan has 138 goals and 127 assists in 470 career games and represented Team USA at the 2014 Olympic Winter Games in Sochi.
The Lightning have also bought out Ryan Malone, so he becomes a free agent. Malone had one year left on his deal which paid him $2.5 million but carried a $4.5 million cap hit.
Acquired from Pittsburgh in June 2008, Malone had 92 goals and 201 points in 342 games with the Lightning. Slowed by injuries, he had five goals and 15 points in 57 games last season.
Malone was charged with DUI and possession of cocaine two months ago after a traffic stop in Tampa.
The Associated Press contributed to this report.