Cusack will voice the title character of Igor, a mad scientist's assistant who secretly harbours dreams of becoming a great inventor. Hayes, who starred in the long-running US series Will & Grace, will voice Igor's sidekick Brian The Brain.
As previously announced, the voice cast includes Steve Buscemi, Jennifer Coolidge, John Cleese, Jeremy Piven, Molly Shannon, and US talk show host Jay Leno.
'John and Sean are both terrific actors and ideally cast in their roles,' Igor director Tony Leondis said. 'We couldn't be more excited to have them join an already fantastic voice cast.'
Cusack also stars for the Weinsteins in the upcoming Stephen King adaptation 1408 as well as Sundance pickup Grace Is Gone. TWC's international chief Glen Basner handled foreign rights sales for Exodus and has virtually sold out all territories.
California-based Exodus' CG-animation slate includes Bunyan & Babe and The Hero Of Color City, which is distributed in North America by Magnolia Pictures.