McClain reports that the extension is worth $26 million, including $10.8 million guaranteed, and contains a $5.25 million signing bonus.
The Texans had until midnight on Monday to pick up the fifth-year option for 2016 on Mercilus' contract, but his new deal will keep him under contract through 2019.
Mercilus has spent three seasons in Houston after being drafted in the first round by the Texans in 2012. The 24-year-old recorded 50 tackles, five sacks and two forced fumbles last season, starting 13 games.
For his career, Mercilus has 115 tackles, 18 sacks and four forced fumbles in 47 games. He's appeared in all but one of Houston's regular season games since being drafted.
The Texans finished 9–7 last season, coming in second in the AFC South.
- Molly Geary