Harrison announced his retirement Monday on Instagram.
Harrison requested his release from the Steelers in December and subsequently signed with New England, where he recorded eight tackles in three playoff games. A recent report suggested he would continue his career, but the 39-year-old linebacker apparently hasn't received any offers to his liking. Harrison did retire once before back in 2014, only to change his mind after the first few weeks of the season. A late-blooming undrafted free agent, Harrison has piled up 793 tackles, 84.5 sacks and 34 forced fumbles in 192 regular-season games, displaying rare longevity for a pass rusher. He played with the Bengals in 2013 and the Patriots at the end of last season, but otherwise spent his career in a Steelers uniform.