Hairston, 25, began his career under Chargers offensive line coach Joe D'Alessandris, who previously coached in Buffalo.
The Bills picked Hairston in the fourth round out of Clemson in 2011, and he appeared in 42 games with the team, starting 15. He played 16 games as a reserve last season, filling in at both left and right tackle.
Hairston announced the move himself with an Instagram post on Wednesday.
- Jeremy Woo