'The Last Man on Earth' is a comedy that comes from Forte and Lego Movie duo Phil Lord and Christopher Miller, The Hollywood Reporter said.
Former 'Saturday Night Live' star Forte, 61, portrays Phil Miller, who is left searching the US for signs of life when an apocalyptic virus wipes out humanity.
Academy Award winner Steenburgen's casting in 'The Last Man on Earth' in a mystery role was announced by Forte at the TCA press tour.
Steenburgen's busy acting schedule also includes appearing in the new season of 'Orange Is the New Black' as corrupt prison guard Pornstache's mother.