Australian writer Helen Garner first learned she was the recipient of a US$150,000 (A$207,633) literary prize after reading an email in her junk folder.

Garner told the Sydney Morning Herald that when she read the email sent from someone at Yale University who had “good news” and wanted her phone number, she thought it was a hoax. Only after checking with her publisher and contacting the university was she able to confirm she had, indeed, won their Windham-Campbell prize for writers.

“I nearly keeled over,” Garner said. “I’m staggered. I feel thrilled and validated.”

Garner was one of nine writers to win the prize, and was not alone in reacting with disbelief. Irish playwright Abbie Spallen told the Irish Times she “thought it was a scam”. Canadian playwright Hannah Moscovitch nearly didn’t listen to the announcement voicemail on her phone. “I thought it was ‘Congratulations, you’ve won a cruise to Florida if you pay $200’,” she told the Globe and Mail.

Established three years ago with a gift from the late novelist Donald Windham, in memory of his partner Sandy M Campbell, the annual prize honours nine writers from any country who write in English, for their “literary achievements or their potential” in fiction, nonfiction or drama. This year’s winners hail from the United States, United Kingdom, Australia, India and Ireland.

The prize is unusual for having no submission process – “no humiliation of applying or being shortlisted, or being in competition with other writers”, Garner told the Sydney Morning Herald. Judged anonymously, the writers are often unaware they are in the running and react with genuine surprise to the bolt-from-the-blue phone call or email they receive from prize director Michael Kelleher.

Garner was recognised for her nonfiction writing, with particular mention given to her 2014 work This House of Grief, which followed the trial of a man accused of deliberately drowning his three young sons by driving his car into a dam. Her upcoming collection of essays, Everywhere I Look, will be released late March.

In a statement Garner said the award “validates in the most marvellously generous way the formal struggles that I’ve been engaged in over the past 20 years. It gives me the heart to keep going”.

The judges commended Garner for her “intelligent, lucid and often disturbing” writing and for bringing “acute observations and narrative skill to bear on the conflicts and tragedies of contemporary Australian life”.

Other winners were Branden Jacobs-Jenkins (United States) in drama; Tessa Hadley (United Kingdom), CE Morgan (United States) and Jerry Pinto (India) in fiction; and Hilton Als (United States) and Stanley Crouch (United States) in nonfiction.

For some of the winners, the unrestricted grant of US$150,000 represents a rare opportunity to write full-time. Jacobs-Jenkins said of the award: “I only wish everyone alive could get a phone call like the one I just received.

“I feel like a fog has lifted and that the writing I want to get done could – for the moment, at least – be less of a negotiation with my day-to-day life.”