Klay obtained the prize on fiction for his book Redeployment, a short stories collection about the life of U.S. soldiers deployed in Iraq, and their way to deal with the devastation of the conflict and the way back home.
“I came back not knowing what to think about so many things,” said Klay, who is himself a marine veteran.
“The book was the only way I knew how to really start thinking it through,” he added, according to British newspaper The Guardian.
In their citation, the judges described the book as a "kaleidoscopic vision of conflict and homecoming" and Klay as the "quintessential storyteller of America's Iraq conflict."
The New Yorker’s staff writer Evan Osnos was awarded with the prize for best non-fiction for Age of Ambition: Chasing Fortune, Truth, and Faith in the New China.
In his book, Osnos, who was correspondent in China for many years, describes the social, political and cultural changes that the country has gone trough in recent years.
Louise Glück, who is considered one of U.S. most important contemporary poets, won the poetry award with his book Faithful and Virtuous Night.
Brown Girl Dreaming, of writer Jacqueline Woodson, won the award for best book for young people. Woodson's book tells, trough poetry, her own story about growing up as an African American in New York and South Carolina during 1960’s and 1970’s.
The National Book Awards, which are administered by the National Book Foundation, were established in 1950 to celebrate the best of American literature. The finalists in the four categories were selected more than 1,400 entries.
Fantasy writer Ursula K Le Guin was awarded with the Medal for Distinguished Contribution to American Letters.
Le Guin, who won the National Book Award back in 1973, gave an emotional acceptance speech, in which she had some harsh words for Amazon's CEO Jeff Bezos.
Bezos pressure tactics against publishers put him in the center of a scandal in the editorial world earlier this year.
“We just saw a profiteer try to punish a publisher for disobedience, and writers threatened by corporate fatwa. And I see a lot of us, the producers, who write the books and make the books, accepting this – letting commodity profiteers sell us like deodorant, and tell us what to publish, what to write,” said Le Guin in her speech.