The "Doctor Strange" star joins an all-star cast that includes David Tennant, Michael Sheen, Jon Hamm, Nick Offerman, Miranda Richardson, Mireille Enos, and Frances McDormand, who will voice the role of God.
Like the "Fargo" star, Cumberbatch will not appear in the series - he will merely be heard as the devil.
"It's a giant animated Satan," "Good Omens" creator Neil Gaiman explains. "He turns up and we needed a performance that works. So we found a young British help... Benedict Cumberbatch."
The writer and filmmaker made the big casting reveal during a Television Critics Association panel on Wednesday, February 13.
"Good Omens" will launch on Amazon Prime Video in over 200 countries on May 31.