Harrison made the announcement on social media, saying he's "missed way too much for way too long ... and I'm done".
Harrison played one season, 2013, with the Bengals and one game in 2017 with the Patriots after being released by Pittsburgh in late December.
New England, in desperate need of help along the edge, scooped up Harrison immediately.
Harrison, 39, spent the majority of his career as a member of the Pittsburgh Steelers. He played 69 snaps in the Patriots' Super Bowl LII loss to the Philadelphia Eagles.
Bill Belichick credited him for his professional approach in the playoffs.
Harrison registered a team-record 80.5 sacks in 13-plus seasons with the Steelers, making five Pro Bowls, twice being named first-team all-pro and earning National Football League defensive player of the year honors in 2008.
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