Downey Jr.'s film credits include "Chaplin," "Iron Man," "Tropic Thunder" and "Sherlock Holmes."
DreamWorks had previously announced Rob Minkoff, who worked on "Stuart Little" and "The Lion King," will direct "Mr. Peabody & Sherman," marking his return to animation after 15 years.
"It's great to come back to my first love, animation," Minkoff said in a statement Wednesday. "The opportunity to make another animated feature with Jeffrey Katzenberg and the amazing team he's built at DreamWorks Animation is truly a dream come true. I've loved the time-traveling adventures of 'Mr. Peabody & Sherman' since I was a kid. There's something irresistibly charming about the idea that the world's smartest person is a dog who adopts a 'pet' boy."
"Rob is a brilliant filmmaker and welcoming him to DreamWorks Animation is exciting for all of us," added DreamWorks Animation's Chief Creative Officer Bill Damaschke. "We look forward to working with him to bring one of the most unusual father-son teams ever conceived to the big screen."