The team did not disclose financial terms, but NFL Network reported the deal to be worth $59.2 million.
Heyward, 26, was in the final year of the rookie contract he signed after being selected 31st overall in the 2011 NFL Draft. He has played in 64 straight games, the third longest streak among defensive ends in the league.
Last year, Heyward shared the team lead in sacks with a career-best 7 1/2, becoming the first Pittsburgh defensive lineman to lead or tie for the most sacks since Aaron Smith in 2004.
"I love this organization," Heyward said in a tweet that included a picture of him signing the contract. "Very blessed and excited about continuing my career as a Steeler! #somanythanks #greatday"