In a tweet, Atwood explains she was inspired to write the book in part to answer readers' questions about the fictional nation she calls "Gilead".
'Well, nearly everything! The other inspiration is the world we've been living in'.
Sonny Mehta, Editor-in-Chief and Chairman, Knopf Doubleday Publishing Group, said The Handmaid's Tale has been in print since its initial publication "due to both Margaret Atwood's brilliant storytelling and the novel's prescient themes".
"The moment the van door slams on Offred's future at the end of The Handmaid's Tale is one of the most brilliantly ambiguous endings in literature. This new book is no exception". It's a connection Atwood was eager to embrace while readying her fans for "The Testaments".
The action in the new book will be separate from the TV series, which is gearing up for a third season.
"In Western society, you don't have to go back very far to find a lot of the things I put in", Atwood said in an interview with The Times earlier this year.
Chatto & Windus said that The Testaments will be published 10 September 2019. An audio book by Penguin Random House also will be available then, and a trade paper edition will be published the following year by Anchor.
The Handmaid's Tale has sold more than 8 million copies since it was first published.
However, it seems unlikely that The Testaments will mirror the plotline of the award-winning The Handmaid's Tale television series, which is produced by Hulu and beamed onto Aussie screens by SBS. The season turned the bleak dial up by 11, putting Offred/June (Elisabeth Moss) through more emotional and physical torture than you could expect for a character who has already been forced into servitude to bear children as a "handmaid" by an oppressive, fundamentalist government.
Atwood never mentions President Donald Trump by name as an inspiration for picking up the tale decades after she left off, but the book is clearly a means to capitalize on the sudden resurgence of interest in the 1985 "feminist classic", according to the BBC.