Narveson is slated to start Wednesday's series finale against the Pirates.
Macha also announced veteran right-hander Jeff Suppan -- and his $12.5 million contract -- will move to the bullpen. Suppan last pitched out of the bullpen in 2003 with the Red Sox.
"I talked to Jeff today and ... he was extremely professional about the whole thing," Macha said. "He said he'd help the club any way that he could."
When asked about it before Sunday's game, Suppan said the move was a bit unexpected after only two starts.
He did not give any indication that he was upset with the decision, however.
"I was surprised a little bit, but ultimately I don't concern myself with it," Suppan said. "I just need to continue to work on what I need to work on to go out and pitch, and that's pitch selection and pitch location. ... It was a situation where they told me today, after two starts, and I'll go to the bullpen and help out any way I can."
Through two starts, both of which came against the Chicago Cubs, Suppan had allowed 10 runs -- nine earned -- in 9 1/3 innings. The Cubs connected for 16 hits, three of which were home runs, off Suppan in the two games.
But did he think two starts was enough of a measuring stick?
"Well, it's really not up to me. It's not my decision," Suppan said. "They have their reasons and they have their thoughts, and I respect that. I'm just a player. I have a locker and they have the big offices. They make the decisions."
General manager Doug Melvin conceded that it "might be unfair" to judge Suppan on only two starts, but nonetheless felt a change was in order.
Usually, such decisions are communicated to the player by the manager or the pitching coach, but given Suppan's tenure with the team and his long Major League career, Melvin wanted to be a part of the discussion Sunday morning.
"As I told Jeff, we're in a situation where the rope's not as long as it used to be with people," Melvin said. "We respect and admire Jeff for what he's done, and I said, 'Hang in there, keep the chin up and you could get back in there, too.' We have to look for as many quality starts as we can from a five-man pitching staff, so somebody else is getting an opportunity."
Narveson earned the spot because of his performance in September 2009 and Spring Training this season, Macha said. Of the three candidates for the fifth-starter role -- Narveson, Suppan and lefty Manny Parra -- Narveson had the best Spring Training by far.
During the spring, he pitched 13 innings over five games and did not allow a run on 10 hits. Suppan and Parra each finished with an ERA of over 5.00.
Narveson has struggled a bit out of the bullpen, though, including Saturday's game in which he allowed three runs to score in the eighth on two hits and two walks. In the ninth, however, he came back and retired the side in order.
He wasn't able Sunday morning to talk about the move back to the starting rotation because Macha had yet to make the official announcement. But Narveson said he was ready for whatever role the Brewers wanted him to fill.
"It's not easy [going back and forth], but I think there's a mentality for it," Narveson said. "You have to be flexible and not set with one thing or another."
After Suppan managed only 9 1/3 innings over his first two outings -- forcing the bullpen to pitch 8 2/3 frames in those games -- Macha and the Brewers are hoping Narveson can give them more innings and quality starts.
"That kind of stuff hampers you," Macha said. "When you get a lot of innings out of your bullpen, that has a residual effect, as it did yesterday."
Jordan Schelling is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.