Former soldier Kevin Powers has won the £10,000 Guardian First Book Award for novel The Yellow Birds (Sceptre).
The book is a fictional depiction of the psychological impact of serving in the Iraq war, informed by the author's own experiences of the conflict.
Chair of the judges Lisa Allardice, editor of Guardian Review, called the book "a powerful meditation on war and morality." She said: "Its subject matter is ugly and harrowing, but its expression is beautiful and poetic. It is a triumphant, unforgettable first novel."
Also judging the 14-year-old prize were authors William Dalrymple, Ahdaf Soueif, Kate Summerscale and Jeanette Winterson, as well as Guardian deputy editor Katharine Viner and Waterstones events co-ordinator Stuart Broom.
Also shortlisted were Chad Harbach's The Art of Fielding (Fourth Estate), Katherine Boo's Behind the Beautiful Forevers (Portobello), Lindsey Hilsum's Sandstorm (Faber), and Kerry Hudson's Tony Hogan Bought me an Ice Cream Float Before he Stole my Ma (Chatto). The shortlist was selected in collaboration with five Waterstones reading groups from around the UK.