Pittsburgh announced the move Tuesday. The No. 30 overall pick in the 2017 NFL Draft is now under contract through 2021.
Watt had 55 total tackles, 36 quarterback hits, 14.5 sacks, 14 tackles for a loss, eight passes defensed, a league-high eight forced fumbles, four fumble recoveries and two interceptions in 16 starts last season.
He has 177 combined tackles, 70 quarterback hits, 36 tackles for a loss, 34.5 sacks, 18 passes defensed, 15 forced fumbles, four fumble recoveries and three interceptions in three seasons with the Steelers. Watt has only missed one start since his rookie campaign.
Watt has a base salary of $1.7 million in 2020. The Steelers can still negotiate for a long-term contract with the linebacker after they picked up the contract option.