"Many thanks to my family, coaches, the fans, and everyone who played a role in my football life", he wrote on Instagram.
"Deebo" included photos of his two sons on his retirement posts.
Harrison was named Defensive Player of the Year for the 2008 season, which he capped with the longest interception return in Super Bowl history, his 100-yard effort helping the Steelers to victory over the Arizona Cardinals in Super Bowl XLIII.
The Ohio native ends his career as a two-time Super Bowl champion and a five-time Pro Bowler.
Harrison, 39, played a total of 15 seasons in the league, spending 13 years with the Steelers during two spells. With reduced playing time during the 2017 season, Harrison requested that the team release him from his contract.
That marked the second Lombardi Trophy of Harrison's career, having also triumphed with the Steelers three years previous against the Seattle Seahawks in Super Bowl XL.
Harrison played almost his entire career with the Steelers and the 84.5 sacks he collected while wearing black-and-gold are a franchise record. He set the Steelers franchise record for sacks in a 2016 game against the Cleveland Browns.