He will be opposed by right-hander Jeremy Hellickson, who was named the Phillies' Opening Day starter on Sunday.
He was chosen over Brandon Finnegan to start the game on April 3 at Great American Ball Park, where he gas pitched only one other time in his career.
"It's pretty cool,'' Feldman said. "I know about the history of Cincinnati, being like the capital of Opening Day.''
Feldman's only appearance at Great American Ball Park was a start for the Cubs on May 24, 2013. He took the loss after going 5⅓ innings and allowing five runs, including a homer by Joey Votto. He also hit a homer off Bronson Arroyo, who is trying to win a spot on the Reds' roster.
The veteran right-hander signed a one-year deal with the Reds in the offseason.
Feldman has pitched for the Rangers, Cubs, Orioles, Astros and Blue Jays. He was used mostly in relief last season, making only five starts, but has been getting ready this spring to return to a starting role.
In 40 appearances last season for the Astros and Blue Jays, he went 7-4 with a 3.97 ERA, with 56 strikeouts and 19 walks.
Feldman will be the Reds' third different Opening Day starter in three years. Johnny Cueto started in 2015, when he was traded to Kansas City. Raisel Iglesias started last season in place of Anthony DeSclafani, who injured an oblique during spring training. Iglesias was moved into the bullpen later in the season.
The Associated Press contributed to this report.