Kiwanuka, who will be 32 next month, has spent all nine seasons of his NFL career with the Giants. He played vital roles on the teams that won Super Bowls XLII and XLIV in 2007 and 2011, respectively.
Kiwanuka's 2014 season ended after 11 games, 28 tackles and 2.5 sacks when he was forced to undergo knee surgery.
Kiwanuka was due a $4.78 million base salary in 2015 and his cap hit would have exceeded $7 million. Prior to last season, Kiwanuka accepted a pay cut to keep his roster spot.
The Giants finished 6-10 last season, the team's worst record since 2004.
- Mike Fiammetta