Redmayne will voice a central caveman character called Dug, in the Nick Park-directed adventure, said The Hollywood Reporter.
"Not only is Eddie a joy to work with, his versatility and boundless energy have really helped to bring my new character to life," said Park.
"He embodies the cheeky charm, fun and plucky wit of Dug, and I'm sure he'll get along brilliantly with Dug's sidekick Hognob."
Set at the dawn of time, when prehistoric creatures and woolly mammoths roamed the earth, "Early Man" tells the story of Dug, along with sidekick Hognob, who unites his tribe against the mighty Bronze Age in a battle to beat them at their own game.