Solar Bones by Mike McCormack was named the winner of the £10,000 award, which recognises fiction  "that breaks the mould".
Published by Tramp Press, the novel follows the recollections of an engineer named Marcus Conway briefly returned from the dead.
McCormack is the third Irish writer to win since the prize began in 2013.
Chairman of judges Professor Blake Morrison said: "Set over a few hours in a single day, and told in the first-person voice of a middle-aged engineer, Mike McCormack's Solar Bones transcends these seeming limits magnificently.
"Politics, family, art, marriage, health, civic duty and the environment are just a few of the themes it touches on, in a prose that's lyrical yet firmly rooted.
"Its subject may be an ordinary working life but it is itself an extraordinary work."
McCormack, 51,  called on more publishers to take risks with experimental authors.
"Readers are smart. They're up for it," he said.
"That was what the people at Tramp Press taught me. There are readers out there and they have been proved right."
The six shortlisted works were:
The prize was founded in 2013 by Goldsmiths, University of London, and is held in partnership with the New Statesman.
Last year's winner was Beatlebone by Kevin Barry.
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A novel written in a single unbroken sentence has won the Goldsmiths Prize 2016.