Harrison spent the majority of his career with the Pittsburgh Steelers, amassing a franchise record 80 1/2 sacks over 14 seasons.
At the end of the season, he entered free agency.
The outside linebacker posted a bunch of pictures to Instagram Monday morning of his kids with the caption: I've missed way too much for way too long.and I'm done.
In August 2014, Harrison announced his retirement, but by September he was back with Pittsburgh.
Harrison turns 40 on May 4.
The Steelers released him late in the season to make room for offensive tackle Marcus Gilbert, who was being activated from a suspension.
Harrison ended up being used a lot more than many anticipated by New England.
He also was the 2008 AP Defensive Player of the Year in helping lead the Steelers to a Super Bowl victory.
Other players who finished decorated National Football League careers with brief stints in New England include Reggie Wayne, John Lynch, Torry Holt and Steven Jackson.