The announced the firing of head coach and general manager on Monday after six-plus seasons with the NFL organization and an 0-4 start this year, per Aaron Wilson of the Houston Chronicle.
Defensive coordinator Romeo Crennel will serve as the team's interim head coach, according to Mark Berman of Fox 26.
The Texans hired O'Brien in January 2014 after he spent two years as head coach of the Penn State Nittany Lions.
The 50-year-old Massachusetts native enjoyed a promising start to his time in Houston. He went 9-7 in each of his first three seasons, the latter two of which resulted in playoff appearances.