The Texans announced the extension Saturday but did not disclose the length of the contract or its financial terms.
Mercilus, Houston's first-round pick in 2012, was set to become a free agent during the offseason. He'll be entering his age 30 season in 2020 but is still producing at a high level.
This season, Mercilus got off to a fast start with five sacks, an interception and four forced fumbles in his first four games. His production then slowed, especially after the season-ending injury to J.J. Watt, who commanded a lot of attention from opposing offensive lines.
Mercilus has 7.5 sacks and two interceptions entering Houston's regular-season finale against the Tennessee Titans.
When coach Bill O'Brien was asked about Mercilus' play after the Texans clinched the AFC South in Week 16, he said he wanted Mercilus back. Since the unexpected firing of general manager Brian Gaine this past summer, O'Brien has taken on even more of a role in Houston's personnel department.
"Whitney is a hard worker," O'Brien said. "I mean, you guys know, Whitney works very hard, puts a lot of time in, and it's important to him. You see him early in the morning, and he stays late. He tries to do whatever he can to do what's best for the team. He is an excellent teammate. We want Whitney back here, and we want him to be a part of our team for a while."
The Mercilus extension helps solidify the Texans' pass rush moving forward. Houston traded Jadeveon Clowney to the Seattle Seahawks right before the start of the regular season, and Watt has struggled with injuries over the past few years. Mercilus has been durable for the Texans aside from a torn pectoral muscle that ended his 2017 season.