A source told ESPN's Adam Schefter the extension is for four years and worth $60.4 million, with $40 million guaranteed. Casey had two years left on his deal.
"I want to make sure I make every play I possibly can," Casey said after signing his extension.
Casey, a 2011 third-round pick, has notched at least five sacks in each of the past four seasons. He made the Pro Bowl the past two seasons.
"It is rare to do a contract extension early in this business," Titans general manager Jon Robinson said. "But Jurrell is a unique player in that he was drafted here, has already done an extension with the team, is a standout in our community and has earned multiple Pro Bowl invitations. We are happy to have him as a Titan for many years to come."
Casey started 15 games last season and set a career high with 29 quarterback pressures in addition to 51 tackles, five sacks and three tackles for loss. He is the first player to register four consecutive seasons with at least five sacks since the team moved to Tennessee in 1999.
"It's a unique case," Titans coach Mike Mularkey said on the deal. "A lot of things played into what happened. There's a lot of on and off the field things that warranted it."
Drew and Jason Rosenhaus, who represent Casey, walked out of the Titans facility with big smiles shortly after the deal was announced. The Titans were in the middle of their training camp conditioning test while Casey was signing his deal.
ESPN's Cameron Wolfe contributed to this report.