The Lions traded the guard to the San Francisco 49ers on Thursday. In exchange, the Lions received a fifth-round pick in 2019, a source told ESPN, confirming multiple reports.
Tomlinson must first pass a physical for the trade to become final.
After the trade was announced, Tomlinson tweeted:
Tomlinson started 24 of 32 games for the Lions in his two seasons in Detroit after being considered one of the best guards in his class. But he never quite fit with what the Lions were trying to do. He eventually lost his starting job to rookie Graham Glasgow midway through last season and only regained it after Glasgow moved to center to replace the injured Travis Swanson.
In dealing for Tomlinson, the Niners added some help to the interior of the offensive line, an area that has emerged as a concern for them in the preseason. With projected starting left guard Joshua Garnett still recovering from a knee injury and his return date uncertain, the Niners have been using Zane Beadles and Brandon Fusco as the starting guards.
While the starting offensive line has done well in pass protection, top running back Carlos Hyde has struggled to find traction. In the three preseason games, he's averaged 2.6 yards on 17 carries in coach Kyle Shanahan's outside zone rushing scheme.
Upon arrival, Tomlinson figures to push for a starting job at guard, likely on the left side where Beadles has been starting in Garnett's absence.
Tomlinson has some ties to the Niners' front office in the form of senior personnel executive Martin Mayhew, who was Detroit's general manager when the Lions used a first-round pick on Tomlinson in 2015.
Tomlinson only received first-team work during training camp this year when right guard T.J. Lang -- who Detroit signed in the offseason from Green Bay -- sat out of practice for rest as he recovers from offseason hip surgery.
The signing of Lang along with the emergence of Joe Dahl as a utility lineman made Tomlinson's future with the Lions cloudy at best and, despite his guaranteed salary, he was not a roster lock for this season. The 25-year-old has two years left on his contract; his base salary of $1,212,296 is guaranteed for this season. Next year's $1,600,944 base salary isn't guaranteed.
This is the second straight preseason where the Lions and 49ers have made a trade. Last year, Detroit sent receiver Jeremy Kerley to San Francisco in exchange for guard Brandon Thomas. Kerley finished the season as the 49ers' most productive wideout.
NFL Network first reported news of Thursday's trade.
ESPN's Nick Wagoner contributed to this report.