A 13-year NFL veteran, Keisel has spent his entire career in Pittsburgh. The 36-year-old was drafted by the Steelers in the seventh round in 2002 out of BYU.
"Brett has played a major role in our success during his 13 years in Pittsburgh," said general manager Kevin Colbert. "We appreciate his efforts and we are grateful for what he helped us accomplish, including two Super Bowl championships. We will always consider him an all-time Pittsburgh Steeler."
Keisel played in 12 games last season before being placed on injured reserve with a triceps injury on Dec. 1.
He has started 114 games in his career and has recorded 408 tackles, 30.0 sacks, seven forced fumbles and two interceptions.
In 2014, Keisel had 17 tackles and an interception before his injury. The defensive end was named to the Pro Bowl in 2010 and won Super Bowl XL and XLIII while with Pittsburgh.
- Molly Geary