Arianna Huffington, columnist and blogger who was among this year's Blooker judges, said Buzzell's book was "endlessly surprising... delightfully profane".
She said it was "an unfiltered, often ferocious expression of his boots-on-the-ground view of the Iraq war".
Buzzell started blogging shortly after being posted to Iraq, writing his website from a cyber cafe in an army tent.
The US Army eventually shut down the blog, but he had already attracted interest from publishers.
"My War tells what it's like to be a grunt fighting in the Sunni Triangle with more power and authority than the best 'embedded reporter' could manage", said Nick Cohen, columnist and Blooker judge.
"It's something of a triumph for blogs over traditional media."
My War won the overall Blooker prize as well as the non-fiction category.
The Doorbells of Florence, by Andrew Losowsky, won the fiction category, while Mom's Cancer, by Brian Fies, won the comics category.
"The success of books like My War reflects the growing recognition of 'trickle-up writing', or writing that starts online," said Bob Young, chief executive of Lulu.com, the Blooker's sponsor.
