On March 1, 2017, Harrison signed a two-year contract extension with the Steelers. Through the first 12 games of the 2017 season, Harrison played only 29 snaps, with 15 of those coming in Week 6 against the Kansas City Chiefs. Following injuries to Ryan Shazier and Tyler Matakevich and the subsequent move of Arthur Moats from the outside to the inside linebacker position, Harrison played 11 snaps in Week 14 against the Baltimore Ravens. On December 23, 2017, Harrison was released by the Steelers after only playing in five games and being a healthy scratch for most of the season.