Butler is in line for a five-year, $61 million deal that includes $30 million guaranteed, and Lewis is expected to sign a four-year, $23 million deal that includes $11.5 million guaranteed, sources told ESPN.
Butler surprisingly didn't play a defensive snap in the Patriots' 41-33 Super Bowl LII loss to the Philadelphia Eagles due to what New England coach Bill Belichick described as a coaching decision.
The hero of Super Bowl XLIX with a game-saving interception against the Seattle Seahawks, Butler spent four memorable years in New England that included notable highs and lows.
An overlooked prospect in 2014 out of Division II West Alabama, he was invited to New England for a tryout and earned a contract on the offseason 90-man roster almost a month after the draft. He rose to unexpected fame with his Super Bowl interception, and the team showed its faith in him the following season, in 2015, by elevating him to the No. 1 spot on the depth chart to replace departed free agent Darrelle Revis.
After being drafted by the Eagles in 2011, the 5-foot-8, 195-pound Lewis joined the Patriots ahead of the 2015 campaign and got off to a hot start that season before tearing his ACL. His recovery ate into his 2016 season, but he showed a return to form in 2017.
Lewis led the Pats with 896 rushing yards on 180 carries (5.0 average) and six touchdowns in the 2017 regular season. He added 32 catches for 214 yards and three receiving touchdowns, while also serving as the team's primary kickoff returner (23 returns, 570 yards, one touchdown).
Lewis' receiving strengths with be a perfect complement to incumbent Derrick Henry, who has a punishing running style. Henry has been anxious for an opportunity to be the Titans' workload back after waiting behind DeMarco Murray for two years. Henry was excited when the role cleared for him with Murray's release.
While Lewis had his moments in the sun with New England, Butler became a full-fledged star after his Super Bowl XLIX pick.
Despite Butler's sudden stardom, Belichick said at one point in 2015 that Butler "as much as any player that I've been around, has really not changed very much from Year 1 to Year 2."
Butler, 28, started every game in 2015 and 2016, earning a Pro Bowl berth in 2015, though his future with the team was uncertain after the 2016 season, when he was a restricted free agent. The New Orleans Saints hosted Butler on a visit but never signed him to an offer sheet.
Butler returned to the Patriots in 2017 and had a self-described up-and-down season that culminated with Belichick's shocking decision not to play him on defense in Super Bowl LII. After the game, in an emotional moment, Butler said the Patriots gave up on him.
Butler's durability was impressive in his time with the Patriots, as he played 98.8 percent of the defensive snaps in 2015, followed by 96.7 and 97.8 the next two seasons. Teammates nicknamed him "Strap" because of his ability to closely cover receivers and also "Scrap" for his scrappy style of play.
Butler and Lewis will play for former Patriots linebacker Mike Vrabel and former Pats personnel man Jon Robinson, who are now the Titans' head coach and general manager, respectively.
Butler's defection to Tennessee marks the second straight year that a Patriots cornerback will have left in free agency to join the Titans. Logan Ryan agreed to a contract with the Titans last offseason.
ESPN's Mike Reiss, Cameron Wolfe and Josina Anderson contributed to this report.