The deal is worth $2.5 million and could rise to $3.35 million with incentives, a source told ESPN's Adam Caplan.
Reyes, 26, led all San Diego defensive linemen in combined tackles (32) and quarterback hits (11) in 2015. He also finished with two sacks and an interception.
Reyes' play during the final six games contributed to the improvement of San Diego's defense during the backstretch of the 2015 campaign.
A second-round selection by the Chargers in the 2012 draft, the University of Connecticut product hasn't missed a game in four seasons. But Reyes hasn't filled up the stat sheet, collecting 13.5 sacks and no forced fumbles in four years.
ESPN Chargers reporter Eric D. Williams contributed to this report.