Miller, the Cardinals' No. 1 overall prospect, will be put in the bullpen, though general manager John Mozeliak said the Cardinals haven't ruled out the possibility that Miller could make a start later this month. For now, though, expect Miller to be used primarily as a long reliever.
"I think he made a lot of strides in the second half of the season in his game," manager Mike Matheny said. "I think, even more so, he made some strides maturing as a player and a person. It really seemed like he turned the corner in the way he was going about it. And obviously, he had a strong finish on the mound.
"Then we look at the fact that we're right in this thing. So we have to have our best. And if he's one of our best right now, then he should be here."
Just a few weeks ago, the Cardinals characterized a callup as unlikely for Miller. But Miller's performance continued to improve, and the Cardinals' situation changed. St. Louis' bullpen has been taxed because of the rotation's string of short starts.
After reaching the All-Star break with a 6.17 ERA, Miller has posted a 2.88 ERA in 10 starts since. He has won seven of those games. The improved results followed some mechanical tweaks and additional reinforcement from the organization that Miller should be less dependent upon his fastball.
"If you look back at how he's pitched over the last six, seven weeks, he's really turned the corner," general manager John Mozeliak said. "When you look at sort of the composition of our club right now in terms of starting pitching and not being able to go deep into games -- we're probably tiring a little bit as we get into September -- we thought he would just be a nice injection into that."
Miller wrapped up his first Triple-A season with a six-inning outing on Friday. The right-hander allowed one earned run on five hits in the effort. He also struck out nine and did not walk a batter. That gave Miller, the Cardinals' top pick in the 2009 Draft, 160 strikeouts in 136 2/3 innings this year.
Miller will have to be added to the team's 40-man roster, though there is already an opening. Also joining the Cardinals on Tuesday will be outfielder Adron Chambers and infielder Ryan Jackson.
Jackson will give Matheny another shortstop option in Rafael Furcal's absence. Adding Chambers injects some speed onto the bench.