The Patriots announced the move on Tuesday, three days after Harrison's unceremonious departure from Pittsburgh. On his Instagram account, Harrison confirmed the signing by posting a photo with #Tom Brady with the caption: "Finally".
Harrison cleared waivers Monday making him a free agent. To make room for Harrison, the Patriots released linebacker Trevor Reilly. Veteran David Harris saw an uptick in playing time when Hightower was lost for the year in Week 7, but did not play on Sunday despite being on New England's active roster.
The Patriots and Steelers played in one of the best games of the National Football League regular season back in Week 15, with the Pats emerging victorious under some dubious circumstances to swipe the top spot in the AFC.
For his career, Harrison has 82.5 sacks and 570 tackles in 15 seasons, 14 of which were spent in Pittsburgh, the other in Cincinnati.
The New England Patriots have won their fourth Super Bowl in the Brady/Belichick Era by defeating the Seattle Seahawks 28-24 in Super Bowl XLIX in Arizona.
This also could be a signing with the Patriots' first playoff opponent in mind.
New England, which won the AFC East for a ninth consecutive season, can wrap up the AFC's top seed with a win over the Jets this weekend or a loss by the Steelers, who host winless Cleveland.
But his role decreased as the Steelers transitioned to more pass-coverage work for outside linebackers Bud Dupree and rookie T.J.
The signing could make for an interesting reunion between Harrison and Pittsburgh should the Patriots and Steelers meet in the AFC championship game.