The longtime star defender posted on Instagram after signing the contract:
Adam Schefter of ESPN reported the deal is worth $3.5 million.
Harrison has been in the NFL for 14 seasons, all but one of those spent with the Steelers. He briefly played for the Cincinnati Bengals in 2013 before returning to Pittsburgh for the past three years.
Although his career has slowed since five straight Pro Bowls from 2007-11, the 38-year-old has remained productive. He finished last season with 53 tackles and five sacks, starting seven of his 15 games.
The linebacker was especially impressive toward the end of the year and postseason, tallying 2.5 sacks in three playoff games.
"I'm not done," Harrison said after the season, per Gerry Dulac of the Pittsburgh Post-Gazette.
Ian Rapoport of NFL Network reported mutual interest in a reunion with the Steelers in February. The two sides finally agreed to a deal and the linebacker will hope to make an impact once again in 2017.
While Harrison should provide depth to the defense, his presence in the locker room is invaluable to this squad. Most of the defense has gotten younger and faster, but the veteran will still have a place on the roster.
After reaching the AFC Championship Game this past season, the Steelers should enter next season as a top contender with Harrison looking for his third Super Bowl title.