Demetri Martin, from New York, was seen by many as the favourite
New Yorker Demetri Martin is the winner of the 23rd Perrier
The American comic, who dropped out of law school to pursue comedy, took the prestigious prize for the best comedy of the Edinburgh Fringe Festival.
He beat New Zealand duo Flight of the Conchords, Australian Adam Hills, fellow American Reginald D Hunter and lone Briton Howard Read.
In the Perrier Best Newcomer Award, the winner was Gary Le Strange.
He beat Alex Horne, Miles Jupp and Michael McIntyre.
Nica Burns, director of the Perrier Comedy Award, described it as "a
breathtaking win" for Martin on his first visit to the UK.
Howard Read brings sidekick Little Howard to life on a computer
The Perrier is the most important comedy award in UK comedy and set comics like Steve Coogan, Al Murray and Frank Skinner on the road to stardom.
Martin said he "was very surprised and excited, if a little overwhelmed and
under-prepared" to have won.
Martin said his challenge had been to try out his comedy show, which is about
self-analysis and obsession, on a UK audience.
"My goal coming here was to see if my material could work in this culture.
"The whole show was a way of trying to develop myself as a performer by doing
something a little bit more confessional, and whether I could do a longer show
from my usual routine."
He added: "I think I learned that when you make your show autobiographical
you start to become tired of yourself, really tired.
"I only managed to fill the void by drinking in bars, eating crepes and snacks and shopping in second-hand stores."
Martin, a Greek-American Yale graduate, created the biggest buzz at this year's Fringe.
He becomes the second American to win the Award after Rich Hall as Otis Lee
Crenshaw, won in 2000.
"Completely unknown here prior to the Festival, Martin beat a shortlist of
unparalleled breadth of style and content in a hotly debated vote," said Ms
He "wrings a strange beauty from geekiness and is at times gloriously funny", according to one critic.
Last year's prize was won by Daniel Kitson while Dylan Moran, Jenny Eclair and The League of Gentlemen have also been winners in the past decade.
This year's award were presented at midnight by two of the 1997 Perrier Award
Winners The League of Gentlemen - Mark Gatiss and Reece Shearsmith - at a ceremony in Edinburgh.