''We talked to him about him being a part of our club, so today was a good morning for him,'' manager Mike Matheny said Monday.
The 31-year-old right-hander agreed to a minor league contract in February and had the right to request his release if not added to the roster by Monday. He will get a $2 million, one-year contract and the chance to earn $500,000 in performance bonuses: $250,000 each for three and six starts.
Under baseball's collective bargaining agreement, St. Louis had until Tuesday to give Villaneuva written notice he would be on the opening-day roster, pay $100,000 retention bonus or release him.
A nine-year veteran with a 45-50 record and 4.26 ERA, Villanueva spent the past two seasons as part of the Chicago Cubs bullpen and starting rotation.
''Having the flexibility that he gives us the ability to be a guy that can be a long man for us, that could step in and throw multiple innings, and could also just come in and get some outs for us as guys need time all that is valuable,'' Matheny said.
Villanueva is 0-2 with a 4.91 ERA in seven exhibition games. He has struck out 11 and walked two in 11 innings.
''I saw more strikeouts than I was expecting to see, which is valuable,'' Matheny said. ''I saw a guy in big situations, when he started getting into a mess, figured out how to get out of it and that's kind of been his M.O. We see a guy that can help us in some tight situations, hopefully get us out of some messes.''