Slowey will flip with lefty Brad Hand, who goes from starter to the bullpen.
When the season opened, both were used as long relievers. But Hand was moved into the rotation when Jacob Turner was placed on the disabled list with a right shoulder sprain on April 9, retroactive to April 4.
"Hopefully, Slowey will go out there and give us some innings," manager Mike Redmond said.
Because of upcoming off days in the next couple of weeks, the Marlins are considering staying with a four-man rotation. They wouldn't need the fifth starter until May 3 at home against the Dodgers. By then, Turner could be off the disabled list.
"We may not need that starter again, for a while," Redmond said.
Slowey will be making his first start since July 8, 2013 against the Braves.
A year ago with Miami, Slowey appeared in 20 games with 14 starts. He opened the season as the No. 2 starter, but also worked long relief in the bullpen.
In his career, Slowey has 104 big league starts.
"Last year, he came in and had some decent starts," Redmond said. "Really, at the beginning of the year I liked the flexibility of having two long guys. That changed when Jake got hurt. Brad had a couple of starts. It was a battle for him. He will go back to the bullpen, and we'll give Slowey a shot. We'll see how that goes, and adjust from there."
As a reliever, Hand threw five scoreless innings. But in his two starts -- both against the Nationals -- he was 0-1 with a 11.37 ERA. He worked 6 1/3 total innings in those starts.
Next week at Atlanta, the Marlins are going with Tom Koehler (Monday), Jose Fernandez (Tuesday) and Nathan Eovaldi (Wednesday).
The Marlins are off on Thursday, and could have gone with Koehler on Sunday against the Mariners, and Fernandez on Monday against Atlanta.
Against the first-place Braves, the Marlins lined up their top three pitchers, in terms of how they've performed thus far.
"We kind of looked at who would be pitching against what team as we went down the road," Redmond said.
Turner, meanwhile, threw off flat ground again on Wednesday, and he is expected to throw off the mound on Friday. Before Turner is cleared to come off the DL, he will make at least one rehab assignment start.