Timberlake joins the previously announced Anna Kendrick, who will voice Princess Poppy.
According to the Hollywood Reporter, Timberlake will voice Branch, a "hardcore survivalist who hides his true colors."
The film is based on the Troll dolls franchise. It will be directed by Mike Mitchell and co-directed by Walt Dohrn. Gina Shay will produce.
"Trolls" will be released Nov. 4, 2016.