Garnett played college football at Stanford, and the 49ers made him the No. 28 overall selection in 2016. He has 22 game appearances and 11 starts through his three NFL seasons and missed all of the 2017 season after landing on injured reserve with a knee injury. All 11 of Garnett's starts came during his rookie campaign in 2016.
Garnett suffered a dislocated finger during training camp last year and didn't make a preseason appearance until the 49ers' final game. A dislocated toe in Week 1 of the 2018 season limited the guard to seven games that year.
San Francisco released Garnett on August 31, 2019.