The six-part series, starring David Tennant, Michael Sheen and Jon Hamm, will premiere on the streaming service 31 May.
Benedict Cumberbatch has also joined the cast as the voice of Satan, opposite Frances McDormand who will play God.
Gaiman, who also acts as the show’s executive producer, revealed on Wednesday (13 February) that the entire series will arrive at the same time.
“Plan for your binge dropping then,” he said at a Television Critics Association panel in Pasadena, California
Discussing Cumberbatch joining the cast, executive producer Douglas Mackinnon said they needed a performer who could give McDormand a “run for her money”.
During the panel, Gaiman was asked about the leading characters, with Tennant being Scottish and Sheen being Welsh.
He said: “The book is quintessentially English. It’s not a British book, it’s an English book.” The author added that it boasts “a peculiarly English sensibility”.
Gaiman said Tennant and Sheen, both seated to his left, brought a PG Wodehouse-like quality to the show.
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Gaiman also said Pratchett, who died in 2015 following a battle with Alzheimer’s, asked him as a “last request” to bring the novel to television.
At the panel, Amazon showed attendees an extended clip from the first episode, showing Sheen – dressed in white with bleached blonde hair and Tennant – dressed in black with his hair in red ringlets – side by side discussing good and evil.
The series is based on the novel Good Omens: The Nice And Accurate Prophecies Of Agnes Nutter, Witch, co-written by Pratchett and Gaiman.
Facing Armageddon, Sheen’s fussy angel and Tennant’s loose-living demon have to form an unlikely alliance after growing fond of life on Earth.
But they have lost the antichrist, an 11-year-old boy unaware that he is meant to bring upon the end of days, forcing them to embark on an adventure to find him and save the world before it is too late.
Additional reporting by agencies.
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