Garnett's time with San Francisco was riddled with injuries, including a knee issue that required surgery and landed him on injured reserve in 2017, a thumb injury in 2018 and a dislocated finger last summer in a training camp he was cut from.
The 25-year-old was the No. 28 overall pick in 2016 and started 11 games for San Francisco as a rookie, by far the most productive season of his career. He's appeared in 22 games with 775 offensive snaps. According to Pro Football Reference, he committed four penalties as a rookie, three holding calls and one false start.
He lost a competition with Mike Person in 2018 for a starting guard spot. In a bit of coincidence, the 49ers got one of their starting guards, Laken Tomlinson, in a trade with Detroit in 2017 after a need was created by Garnett's knee injury.
The Lions have a hole at right guard with Graham Glasgow, a versatile lineman who made 58 starts over four seasons at center and both guard spots, heading to free agency after being rotated with Joe Dahl and Kenny Wiggins throughout this season.
The 6-foot-5, 305-pound Garnett played college football at Stanford and won the Outland Trophy in 2015.
Garnett was out of the NFL in the 2019 season.