Eleanor Catton, a Canadian-born writer who grew up in New Zealand, was named the winner of this year's Man Booker Prize on Tuesday evening at a gala reception in London.

Ms. Catton, 28, is the youngest-ever Booker winner. She takes home the award for The Luminaries, an epic-length Victorian-era murder mystery set amid the 1860s New Zealand gold rush that is structured on the astrological zodiac.

The novel, the longest ever to win the prize, "slowly but deeply staked its claim upon us," said Robert Macfarlane, chair of the judges.

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"At 832 pages, it might seem like one of Henry James's big, baggy monster novels. In fact, it's as intricately structured as an orrery. It requires a huge investment of time from the reader, but the dividends it offers are astronomical."

Ms. Catton is also a finalist for a Canadian Governor-General's Literary Award, to be announced next month.

Considered one of the most prestigious literary prizes in the world, the Booker is worth about $87,000, or £52,500.

Now in its 45th year, it is awarded to an English-language novel written by a citizen of the Commonwealth or the Republic of Ireland.

Starting next year, the citizenship restrictions will no longer apply.

Accepting the award at the conclusion of a black-tie dinner at London's Guildhall, whose guests included the Duchess of Cornwall, Ms. Catton touched on some of the issues she explores in her novel, including the tension between the economic value and the inherent worth of something.

During the writing process, "I was free throughout to concern myself with questions not of value, but of worth," Ms. Catton said, praising the support of her British publisher, Granta Books, and her New Zealand publisher, Victoria University Press.

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"This is all the more incredible to me because The Luminaries is, and was from the very beginning, a publisher's nightmare. The shape and form of the book made certain kinds of editorial suggestions not only mathematically impossible, but – even more egregious – astrologically impossible."

To laughter from the audience, she added, "A very sensible e-mail from one of my two editors … might end in the very annoying and not at all sensible reply: 'Well, you would think that, being a Virgo.'"

Ms. Catton follows the previous Canadian winners Michael Ondaatje (The English Patient, 1992), Margaret Atwood (The Blind Assassin, 2000) and Yann Martel (Life of Pi, 2002). She is the second New Zealand novelist to take home the prize, after Keri Hulme's The Bone People in 1985.

Ellen Seligman, the publisher of McClelland & Stewart, Ms. Catton's Canadian publisher, said: "We are hugely thrilled that Eleanor Catton has received this significant honour, recognizing her special artistry and maturity as a writer, both of which belie her young age."

Born in London, Ont., Ms. Catton moved at age six with her family to Christchurch, New Zealand, after her father, an American, got a teaching position at the University of Canterbury.

In a recent interview with The Globe, Ms. Catton spoke of her affinity for Canada.

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"I do feel that my Canadian identity growing up was something that was really important to me, especially as a child. Because I was the only Canadian in my family, I felt a special connection to the country."

She added that she and her partner, the U.S. poet Steven Toussaint, almost moved to Montreal a couple of years ago, after he was offered a position as a PhD student at McGill University. (Instead, the couple moved to Auckland after she was offered a residency there.) "I'm not sure what's going to happen in the next 10 years, but I would love to pursue that further."

Writing in The Globe and Mail, reviewer Pasha Malla said of Ms. Catton's novel: "Despite its length, there isn't a sentence that feels weak or lazy, and by all objective criteria, The Luminaries is a remarkable accomplishment."