This will be Ratner's first involvement with the Oscar show and Mischer's second: He produced and directed the 2011 Academy Awards telecast and was nominated for an Emmy for his work on the show.
Academy president Tom Sherak made the announcement Thursday.
Mischer said in an interview that he's excited to oversee the Oscars again.
"I was just so happy to receive the call from the academy saying we'd like to have you come back," he said. "It was unexpected and a real delight. More than anything, I'm looking forward to working with Brett."
Ratner said producing the Oscar show is "beyond a dream come true."
"This wasn't even in my dreams, it's so far out," he said. "This is something I never could have imagined."
Ratner has produced and directed both film and television. His credits include "X-Men: The Last Stand," "Rush Hour" and the pilot of TV's "Prison Break."
Mischer is a veteran producer and director of live television events, including Super Bowl halftime shows, Olympics opening ceremonies, the Emmy Awards and this year's Oscars.
Dawn Hudson, chief executive of the Academy of Motion Picture Arts and Sciences, said she is eager to see Mischer's expertise blend with Ratner's "smart and fresh take for the show."
"They have great chemistry," she said, "and their vision meshed so well with ours."
The two men declined to reveal their plans. They said they haven't discussed potential hosts for the show.
"Everything is open at this point," Mischer said. "We're just at the starting gate."
He said they plan to watch past telecasts and "figure out what we can do to make things better."
Ratner said they plan to start working on the show immediately. "Work begins now," he said. "We're going to hang up the phone and get to work."
The 84th annual Academy Awards will be presented at the Kodak Theatre on Feb. 26, 2012.