David Conley, 48, is being held with no bond, Harris County Sheriff's Chief Deputy Tim Cannon told reporters.
"Once again, a senseless tragedy has struck our community," he said. "Our hearts go out to the family and friends of those lost."
The incident started late Saturday night after authorities responded to a call to perform a check on the residence, said Thomas Gilliland, a spokesman for the Harris County Sheriff's Office.
When the deputies arrived at the scene, they tried to summon someone to the door, but no one showed up, Gilliland said.
"Information was obtained that a male was in the home and had a warrant for an aggravated assault on a family member," the spokesman said.
Deputies surrounding the house saw a child's body through the window and decided to enter the home, according to Gilliland. The suspect started shooting from inside the house, forcing them to pull back and wait for hostage negotiators and a unit that specializes in high-risk situations.
Negotiators then talked the suspect into coming out and then arrested him, Gilliland said.
"Upon entering into the home ... to check for the welfare for any other people in the house, the bodies of eight victims were found inside the residence," he said.
The victims' ages ranged from 6 to 50 and included a woman, her husband and their six children, according to Cannon. Authorities had initially said that five children and three adults were found dead. All were shot.
Cannon said the suspect's motives appear to be related to the woman, who was his former domestic partner. According to the lead investigator in the case, one -- and possibly two -- of the children killed might have been the suspect's child.
A relative of the woman made the initial call to perform a check on the residence, the investigator said.
The spokesman said authorities have been called to the home before, but the nature of those calls was not immediately available.
An investigation is ongoing.