Miami will receive a 2020 fourth-round pick along with a 2019 seventh-round pick in exchange for Tannehill and a 2019 sixth-round pick.
Tannehill will become a well-accomplished backup for Marcus Mariota in Tennessee, replacing Blaine Gabbert. Titans general manager Jon Robinson said he informed the veteran QB that he will be released.
Miami has a huge quarterback void to fill and seems likely to look toward the draft to do so.
The Titans restructured Tannehill's contract into a deal that will pay him $7 million fully guaranteed with a chance to make up to $12 million in incentives for the 2019 season, a source told ESPN. The deal was made easier for Tennessee since Miami will pay $5 million of the guaranteed money in the form of a signing bonus, a source told ESPN's Adam Schefter.
The Dolphins decided to move on from Tannehill earlier this offseason, and they've spent the past few weeks actively pursuing a trade.
Tannehill was originally due $18.7 million in salary in 2019 and was set to count as $26.6 million against their salary cap. Miami, in the midst of a rebuild, couldn't justify those huge numbers for a player who clearly wasn't part of their long-term future.
Tannehill will leave a $13.4 million dead cap hit on the Dolphins' salary cap in 2019 plus the effects of the $5 million signing bonus they paid to execute the trade. But they did get trade value out of a player they were set to release this offseason, and it will clear their salary cap even more for 2020 -- a big year for the Dolphins as they progress through their rebuild.
"We would like to thank Ryan for his commitment to the Miami Dolphins over the last seven seasons," Dolphins general manager Chris Grier said. "Ryan is a tireless worker who always put the team first. We wish him the best with the next step of his career."
Tannehill now reunites with veteran defensive end Cameron Wake, who signed a three-year, $23 million deal with the Titans earlier this week.
The 30-year-old Tannehill has been the Dolphins' starting QB since he was drafted with the eighth overall pick of the 2012 NFL draft out of Texas A&M.
He's 42-46 as a starter, with a 62.8 percent completion rate, 20,434 passing yards, 123 touchdowns and 75 interceptions. He completed 64.2 percent of his passes for 1,979 yards, 17 touchdowns and 9 interceptions in 2018.
Tannehill's time in Miami was marked by his lack of availability due to injury and inability to get the Dolphins over the playoff hump. Tannehill has missed 25 games over his past three seasons due to a variety of injuries, including a right shoulder capsule injury that cost him five games in 2018.
The injuries also sapped some of what made Tannehill an intriguing quarterback early in his career: athleticism, ability to make plays when they break down and a strong arm with precise accuracy.
For the Titans, they've been looking for multiple seasons to find a top-end backup as injury insurance for Mariota. Titans general manager Jon Robinson got creative in a trade to find the best option to fill the role.
Mariota, 25, hasn't played a full 16-game season in his career. He's also playing on a fifth-year option worth $20.9 million, and he's set to be a free agent after the season.
Tannehill's skill set should fit well behind Mariota as both players rely on accuracy and movement to succeed.
Gabbert had appeared in eight games, including three starts last season for Tennessee. He completed 60 percent of his passes for 626 yards with four touchdowns and four interceptions.
The Titans played the Dolphins in each of the last four seasons with Tannehill playing in three of those games, going 2-1 against Tennessee. Robinson likely got a good look then of what he's getting in Tannehill, who has proved to be at minimum one of the NFL's best 32 quarterbacks when healthy.
The Dolphins spent seven years trying to get a full evaluation of Tannehill, and ultimately they decided it would be a counterproductive same-old-Dolphins way of thinking to let him get another shot under a new staff. Brian Flores was hired to replace Adam Gase as head coach after the season ended.
The Dolphins now face a new era without a clear answer at quarterback. They have been actively examining quarterbacks in the 2019 NFL draft class, and they seem to be a strong candidate to select a prospect in the first round of this year's draft or the next one.
Miami will be looking for a veteran quarterback in the coming weeks to add to the roster. Top available free agents include Colin Kaepernick, Blake Bortles, Ryan Fitzpatrick, Robert Griffin III, AJ McCarron and Mike Glennon.
Information from ESPN's Turron Davenport was used in this report.