Terms of the deals weren't disclosed.
With Tuesday's moves, Houston has signed five free agents from other teams and six of its own.
"Well, we only had four or five guys on our roster, and we definitely needed some depth to our linebacker crew," Texans linebackers coach Johnny Holland told the team's official Web site. "These were two really good additions for us. I think they bring speed and leadership qualities to our group, and we're very excited about having them."
"I like his motor," Holland said. "I like his intensity, and I like what Buster brings to the table as far as his personality. He's a tough guy. So we're looking forward to him coming in and being really productive at special teams for us and playing 'MIKE' linebacker and playing any position as needed. We're very excited to have him."
The 6-foot-4, 309-pound Butler was claimed off waivers by the Texans two years ago and played in eight games over two seasons.
The Associated Press contributed to this report.