Harvey beat five other finalists including Australian author Charlotte Wood who missed out for her novel Stone Yard Devotional, about a woman who abandons her marriage, job and home in the city to live in a cloistered religious community.
Harvey was awarded the Stg50,000 ($A97,692) prize for what she has called a "space pastoral" about six astronauts circling the earth, which she began writing during COVID-19 pandemic lockdowns.
The confined characters loop through 16 sunrises and 16 sunsets over the course of a day, trapped in one another's company and transfixed by the globe's fragile beauty.
"To look at the earth from space is like a child looking into a mirror and realising for the first time that the person in the mirror is herself," Harvey said as she accepted the Booker trophy on Tuesday.
"What we do to the earth we do to ourselves."
She dedicated the prize to "everybody who does speak for and not against the Earth, for and not against the dignity of other humans, other life".
"All the people who speak for and call for and work for peace – this is for you," she said.
Writer and artist Edmund de Waal, who chaired the five-member judging panel, called it a "miraculous novel" that "makes our world strange and new for us".
Gaby Wood, chief executive of the Booker Prize Foundation, noted that "in a year of geopolitical crisis, likely to be the warmest year in recorded history," the winning book was "hopeful, timely and timeless".
Harvey, who has written four previous novels and a memoir about insomnia, is the first British writer since 2020 to win the Booker.
The prize is open to English-language writers of any nationality and has a reputation for transforming writers' careers.
Previous winners include Ian McEwan, Margaret Atwood, Salman Rushdie and Hilary Mantel.
De Waal praised the "crystalline" writing and "capaciousness" of Harvey's succinct novel – at 136 pages in its UK paperback edition, one of the shortest-ever Booker winners.
"This is a book that repays slow reading," he said.
The judges spent a full day picking their winner and came to a unanimous conclusion.
American writer Percival Everett had been the bookies' favourite to win with James, which reimagines Mark Twain's Huckleberry Finn from the point of view of its main black character, the enslaved man Jim.
The other finalists were US writer Rachel Kushner's spy story Creation Lake, Canadian Anne Michaels' poetic novel Held and The Safekeep by Yael van der Wouden, the first Dutch author to be shortlisted for the Booker.
28°C