The action adventure show from Russell T Davies and Phil Ford (The Sarah Jane Adventures, Doctor Who) launches this autumn.
© BBC
"Wizards Vs Aliens is hugely exciting and has a feeling of total originality," Blessed said. "It is full of vision and brilliance.
"The earthly realistic scenes are so heartfelt and moving, and they contrast vividly with the universal feel of the Nekross King and his subjects.
"I find the whole concept miraculous and I am thrilled to be part of such an exciting project."
© PA Images / Matt Crossick/PA Archive
© Mark J. Terrill/AP/Press Association Images
Wizards Vs Aliens centres around the battle between magic and science as a 16-year-old boy enters the battle between the magic-feeding aliens the Nekross against Earth's wizards for the last remaining magic in the universe.
Davies has previously called the BBC Cymru Wales production a "wild, funny, thrilling and sometimes scary collision of magic and science fiction".
He added: "Wizards have never met aliens before, and when they do, the result is spectacular! The mysterious Nekross know exactly what to do with magicians. Eat them! Let battle be joined!"
