The Cardinals released Mathieu on Wednesday after he declined to take a pay cut.
Mathieu was cut just hours before $5.75 million of his 2018 salary and $8 million of his 2019 salary were to be guaranteed.
When healthy, Mathieu has been considered one of most dynamic defenders in the NFL. He has a reputation for having a nose for the football and plays with a reckless abandon that helped shape who he was as a safety. The 5-foot-9 Mathieu became known as one of the best nickel defenders in the league, preferring to play in the box, where he felt he could make an impact on every play, rather than roaming the secondary.
However, Mathieu's promising career in Arizona was marred by injuries.
Mathieu, 25, finished three of his five seasons on injured reserve thanks to two major knee injuries -- a torn ACL and LCL in 2013 and a torn ACL in 2015. Mathieu's 2015 knee injury derailed the best season of his career. When he went down in Week 15 -- in the game where the Cardinals clinched their most recent NFC West title -- he was in the conversation for Defensive Player of the Year. He was named a first-team All-Pro and to the Pro Bowl that season.
His 2016 season was cut short by a shoulder injury that landed him on injured reserve.
Last season was the first in which Mathieu played in all 16 games as he continued to recover mentally and physically from the past injuries.
The Texans struggled last season after safety Quintin Demps left in free agency in March 2017. The unit finished with the top-ranked passing game in 2016 but fell to 24th last season after cornerback A.J. Bouye left for the Jacksonville Jaguars.
Mathieu, a former LSU standout and New Orleans native, will start right away at strong safety for Houston, alongside free safety Andre Hal. The Texans hope that adding Mathieu and cornerback Aaron Colvin, along with the returns of J.J. Watt and Whitney Mercilus as part of the pass rush, will help the secondary in 2018.
While the signing has yet to be made official, Mathieu tweeted to a number of Texans players, including Watt and quarterback Deshaun Watson.
Let's go with the motion! No looking back! https://t.co/71l5IdeXZP— Tyrann Mathieu (@Mathieu_Era) March 17, 2018
LETS GO BRO!! https://t.co/6DWHO0Qinw— Tyrann Mathieu (@Mathieu_Era) March 17, 2018
Mathieu was suspended by LSU before the 2012 season for failing drug tests and then was arrested on drug-related charges that October before leaving school to begin preparing for the NFL draft. He missed the entire 2012 season, leading to him fall to the Cardinals in the third round of the 2013 draft.
In 66 career games, Mathieu has 303 tackles, 25 pass breakups, 22 passes defensed, 11 interceptions, 4 sacks and 4 forced fumbles.
ESPN's Josh Weinfuss contributed to this report.