Harrison has spent all but one season of his 15-year career in black and gold.
The 39-year-old signed a two-year, $3.5-million extension in March, but has appeared in just five games this season. He has shared his disappointment with his lack of playing time and said in early December he wouldn't have re-signed had he known he would spend most of the season on the bench.
"There was no animosity or bad feelings. It's just the business of the NFL," Harrison's agent, William Parise, said after the move, according to ESPN's Josina Anderson. "I believe he still wants to play. We'll have to wait and see what happens with waivers."
Harrison posted a note to Instagram Saturday thanking Steelers fans for their support.
There remains a possibility Harrison could return to Pittsburgh if he clears waivers.
It would cost another team $70,588 to claim Harrison off waivers, according to Albert Breer of Sports Illustrated. Signed to a two-year deal, Harrison isn't owed any guaranteed money for 2018, according to Adam Caplan of SiriusXM.
The Steelers officially released Harrison in order to make room on the roster for tackle Marcus Gilbert, who returns from a four-game suspension for PED use.
The move comes ahead of the penultimate game of the season, as Pittsburgh prepares for a playoff run.
Harrison's 80.5 sacks are the most in team history. He also has 554 career tackles and seven interceptions with the team.
His 100-yard interception-return touchdown in Super Bowl XLIII is one of the most memorable plays of the linebacker's career.