It marks the second time Robertson has changed schools.
A former four-star prospect, Robertson started out at Cal on a promising note, catching 50 passes for 767 receiving yards and earning freshman All-America honors in 2016.
But he received a medical redshirt during his second season on campus and ultimately transferred to Georgia.
He missed multiple games with another injury in 2018 and didn't catch a pass in nine total appearances with the Bulldogs.
His second season in Athens was more productive, as he started four games and caught 30 passes for 333 yards and three touchdowns.
But last season he saw his role diminish, and he caught just 12 passes in 10 games.
Robertson will get a fresh start at Auburn under new coach Bryan Harsin, who comes to the SEC after seven seasons as head coach at Boise State.
What's more, the Tigers' top three receivers from last season -- Seth Williams, Anthony Schwartz and Eli Stove -- have all moved on to pursue careers in the NFL.
Auburn is scheduled to open the season on Sept. 4 at home against Akron.