The contract includes $2 million in performance bonuses.
Hampton spent six seasons with the Astros, ending in 1999 when he won a career-high 22 games and was an All-Star. He was traded to the Mets and won 15 games in 2000 before signing a $121 million, eight-year contract with Colorado.
The big deal proved to be one on the worst free-agent signings ever, with Hampton going 56-52 with a 4.81 in just 147 starts for the Rockies and Atlanta, who acquired him after the 2002 season.
Hampton sat out the 2006 season after Tommy John surgery and did not pitch in 2007 because of an oblique injury and an elbow problem that required season-ending surgery.
Hampton went 3-4 with a 4.85 ERA in 13 starts for the Braves this year. At the end of the season, he expressed interest in returning the Astros.
Despite the difficulties, the 36-year-old Hampton said he never thought about quitting.
"I just knew that I was going to get there," he said. "I was never going to give up. That was not an option. I'm glad I didn't because I'm here today in a great place to play. A place I wanted to play."
General manager Ed Wade expects Hampton to upgrade Houston's rotation by making 35 starts this season.
"A healthy Mike Hampton has always been a workhorse on the club," Wade said. "Mike just finished the season with Atlanta having not missed a start down the stretch second half of the season, the last nine starts being very, very solid. So I don't think there's any reason based on the performance at the end of the season, based on the medical information that we gathered ... for us to feel that he's not going to be able to go out there every fifth day and answer the bell for us."
After sitting out for two full seasons, Hampton said it took a few starts for him to "get the rust off" and feel good on the mound last year.
"After three starts I could finally start turning the corner and I really felt like the velocity picked up, the movement was there," he said. "Toward the end of last year I made 13 starts and I wish I had another 20 because I was feeling that good. I was really excited about where I was and I thought my stuff was there."
Astros manager Cecil Cooper thinks Hampton will add needed experience to his pitching staff.
"I think he could help guys like Wesley Wright and Wandy Rodriguez, being a left-handed pitcher," Cooper said. "I think he'll help those guys and their maturity and their growth."
Hampton chose to wear No. 11 in Houston after longtime catcher Brad Ausmus gave the OK. Ausmus wore the number in his eight years with the Astros, but is likely headed for retirement.
Ausmus hit a home run off Hampton in Houston's season finale this year. The catcher made Hampton promise to share some kind words about him in exchange for the number.
"I wanted to take this number while it was hot," Hampton joked. "He's definitely one of the hottest hitters in the league after that last game and I just hope I can fill it half as good as he did."
Hampton is 141-105 with a 4.01 ERA lifetime. He began his major league career in Seattle in 1993, going 1-3