Ingrid Carlberg, permanent secretary of the Swedish Academy, said the author was in Iceland "listening to the wind" when the academy reached her to notify her of the win.
"She was very taken by surprise," Carlberg said on Thursday.
Toronto-born Carson, 76, draws on themes and stories from ancient Greek and Roman literature for works that often blend elements of poetry, essay and fiction.
Her books include Eros the Bittersweet, a look at the pleasure and pain of desire in ancient Greek literature, verse novel Autobiography of Red, Men in the Off Hours, a collection of poetry and prose that won Canada's Griffin Prize for poetry in 2001 and Norma Jeane Baker of Troy, which compares Marilyn Monroe and Helen of Troy.
Carson also has translated works of classical Greek literature that, the Swedish Academy said, "may be regarded as independent works in their own right".
They include If Not, Winter, based on poem fragments by Sappho, Sophocles' tragic plays Electra and Antigone and Euripides' Bakkhai.
"Almost all her literary production has centred upon the intersection between the philologist's obsession with words and the poet's desire for new meaning," said Anders Olsson, chair of the literature committee.
Carson has taught classics at several North American universities and has lived in Iceland, where she and her husband, Robert Currie, were granted citizenship in 2022.
The prize was announced by the Swedish Academy in Stockholm.
The Associated Press' efforts to reach Carson's literary agent, Nicole Aragi, were not immediately successful.
In 2025, Hungarian writer Laszlo Krasznahorkai, whose surreal and anarchic novels combine a bleak world view with mordant humour, won the Nobel Prize in literature for work the judges said upheld the power of art in the midst of "apocalyptic terror".
Three science awards were announced earlier this week.
The Nobel for medicine went to three scientists whose work led to a tool that uses light to help unravel how the brain works.
The physics award recognised a scientist's efforts to demystify a rare group of neutrinos.
The chemistry prize recognised two scientists for untangling mysterious mirror images in molecules, a discovery that has been used to develop countless drugs.
This week ends with Friday's peace prize.
The Nobel Memorial Prize in Economic Sciences will be announced on Monday.
The prize money is 12 million Swedish kronor (about $A1.7 million).
