Hairston, 26, signed a one-year, prove-it deal to play for the Chargers in free agency last season, and he outperformed the contract.
The Clemson product played through nagging abdominal and ankle injuries, participating in a total of 739 snaps on offense. Hairston started nine games at left tackle, one game at right guard and one game at left guard.
Hairston saw time at all four offensive-line positions during the regular season for San Diego. The only position he didn't play was center. Chargers quarterback Philip Rivers singled out Hairston's toughness during the year.
Chargers general manager Tom Telesco has now brought back Hairston, starting right tackle Joe Barksdale and backup guard Kenny Wiggins in free agency to an offensive line that underperformed and struggled to stay healthy last season.
The Chargers used 24 different offensive line combinations in 2015, fourth most in the NFL.
San Diego fired offensive line coach Joe D'Alessandris and hired Jeff Davidson in his place, who worked with head coach Mike McCoy when both were with the Carolina Panthers.
As of right now, San Diego's projected offensive line from left to right is King Dunlap at left tackle, Orlando Franklin at left guard, Chris Watt at center, D.J. Fluker at right guard and Joe Barksdale at right tackle.