Hargreaves was released by the Bucs on Tuesday after he was benched last weekend for what coach Bruce Arians deemed a lack of hustle.
"He didn't look like he was hustling to go in for a tackle," Arians said when asked about Hargreaves, who surrendered a 55-yard catch to Andy Isabella at the beginning of the third quarter against the Arizona Cardinals on Sunday. "He was chasing somebody across the field, and he wasn't running fast enough."
It is the latest move by the Texans to bolster their secondary. They acquired Gareon Conley from the Oakland Raiders on Oct. 21 in exchange for a third-round pick. Conley was selected in the first round of the 2017 draft; Hargreaves was a first-round pick in 2016.
Hargreaves, 24, joins a secondary that has been dealing with injuries for much of the season. Veteran cornerback Johnathan Joseph has been playing through shoulder and neck injuries, and cornerback Bradley Roby has missed the Texans' past three games with a hamstring injury. Rookie corner Lonnie Johnson also missed Week 9 with a concussion.
The Texans have allowed 277.3 passing yards per game, which ranks 29th in the NFL.
Hargreaves, the 11th overall pick in 2016, was the Bucs' top cornerback heading into this season.
Although he posted an interception in Week 1 and made a game-saving tackle on Christian McCaffrey on a goal-line stand in Week 2, Hargreaves, who was expected to be a leader, appeared to lack focus at times.
The Texans also waived cornerback Briean Boddy-Calhoun from the active roster.
ESPN's Jenna Laine and Sarah Barshop contributed to this report.