This story has been updated.

Breaking the Booker Prize rules, the judges named both Margaret Atwood and Bernardine Evaristo winners of the 2019 Booker Prize on Monday night in London.

Atwood won for “The Testaments,” her long-awaited sequel to “The Handmaid’s Tale.” Evaristo won for “Girl, Woman, Other.”

The Booker Prize has been shared only twice before, but that was before the early 1990s when the rules were changed to explicitly forbid sharing the prize. Peter Florence, chair of this year’s judges, announced to a shocked audience, “We found that there were two novels that we desperately wanted to win this year’s prize.”

This is the second Booker win for Atwood, a 79-year-old Canadian writer who won in 2000 for “The Blind Assassin.” In the prize’s 50-year history, she is only the fourth author to have won twice, but over the years, several of her novels, including “The Handmaid’s Tale” (1985), have been shortlisted.

Evaristo, a 60-year-old Anglo-Nigerian writer who lives in London, is the first black woman to win the prize since it began in 1969.

Coming to the stage with Evaristo to accept her half of the prize, Atwood said: “Neither of us expected to win this. I’m very surprised. I would have thought that I was too elderly. And I kind of don’t need the attention, so I’m very glad that you’re getting some. That makes me happy. It would have been quite embarrassing for me, as a good Canadian, if I had been alone here.”

Atwood and Evaristo’s shared win of the Booker Prize comes just a week after Peter Handke and Olga Tokarczuk both won separate Nobel Prizes in literature.

Atwood, the author of dozens of books — including novels in a variety of genres, works of nonfiction, children’s books and collections of short stories and poetry — is one of the most prominent writers in the world and is rumored to be a perennial contender for the Nobel Prize in literature. Aside from “The Handmaid’s Tale,” considered one of the greatest dystopian novels of the modern era, her best-known books include “Cat’s Eye” (1988), “Alias Grace” (1996) and the MaddAddam Trilogy (2003-2013), a work of speculative fiction about the dangers of environmental destruction and genetic experimentation.

Oddsmakers in Britain, who follow the literary prize intensely, had predicted Atwood would win the Booker this year. Among her competitors were former Booker winner Salman Rushdie and the Turkish British writer Elif Shafak. The Booker Prize — worth about $63,000 — recognizes the best novel written in English and published in the United Kingdom and Ireland.

As one of the world’s top literary awards, the Booker has a reputation for dramatically boosting the winner’s sales, but “The Testaments” has already been a runaway bestseller since it was published on Sept. 10. In the United States, Penguin Random House said that “The Testaments” sold more than 125,000 copies in its first week, with the best opening-day sales of any book in 2019.

“Girl, Woman, Other,” Evaristo’s eighth work of fiction, will be published in the United States on Nov. 5. Evaristo has also published essays and written for BBC radio. “Girl, Woman, Other” follows 12 characters, most of them black, in modern Britain. Writing in the New Statesman, one critic said Evaristo is the novelist to read “if you want to understand modern-day Britain.”

Reflecting on the paucity of minority characters in fiction, Evaristo wrote last week in the Guardian: “What, then, does it mean to not see yourself reflected in your nation’s stories? This has been the ongoing debate of my professional career as a writer stretching back nearly 40 years, and we black British women know that if we don’t write ourselves into literature, no one else will.”

Atwood, an indefatigable writer with nearly 2 million Twitter followers, has been conducting a whirlwind book tour for packed audiences on both sides of the Atlantic. She paused only briefly when her longtime partner, the novelist Graeme Gibson, died on Sept. 18.

For decades, Atwood resisted writing a sequel to “The Handmaid’s Tale,” her classic feminist dystopia about a country called Gilead in which fertile women are enslaved to produce children. But the election of Donald Trump revived fears about the possible loss of reproductive freedom, which pushed the novel back onto the U.S. bestseller list. And then the award-winning Hulu TV adaptation starring Elisabeth Moss brought the story to millions more. Beset by questions about what happened next in the totalitarian society she’d created, Atwood finally relented and began work on a novel that, as she tweeted, was inspired by “everything you’ve ever asked me about Gilead and its inner workings.”

“The Testaments” is a far more hopeful and witty novel than “The Handmaid’s Tale.” It opens 15 years after the close of the previous novel, which ends without revealing what will happen to the narrator, a rebellious handmaid named Offred. The sequel employs three narrators, most notably, Aunt Lydia, a matriarchal tyrant who trains women to be obedient and passive handmaids. As we follow her secret journal entries, we learn how the society of Gilead was constructed — and how she plans to bring it down.

Although the Booker Prize is meant to recognize the supreme quality of a single novel, today’s win for Atwood is surely more of a lifetime achievement award. Although “The Testaments” is an exciting thriller that wraps up many questions for fans of “The Handmaid’s Tale,” it is not a particularly impressive work of literature on its own. But Gilead has seeped into our political consciousness as deeply as the horrors envisioned by George Orwell in “1984.” Protesters around the world now dress as red-cloaked handmaids, most notably at the Supreme Court confirmation hearing for Brett M. Kavanaugh earlier this year. So few novels achieve that level of cultural power that it seems appropriate for the Booker judges to recognize the sequel to “The Handmaid’s Tale.”

For 18 years, the Booker Prize was sponsored by Man Group, a U.K. financial services firm, and called the Man Booker Prize. Earlier this year, the Crankstart charitable foundation took over funding of the prize and its name was again shortened to the Booker Prize. The winner of the prize is chosen by a panel of five judges, which this year included Florence, Afua Hirsch, Liz Calder, Xiaolu Guo and Joanna MacGregor.

Ron Charles writes about books for The Washington Post and hosts