Costa Book of the Year won by Fairweather's The Volunteer

Jack Fairweather's The Volunteer (W H Allen) won the £30,000 Costa Book of the Year, the same week the world marked the 75th anniversary of Auschwitz's liberation.

The Volunteer: The True Story of the Resistance Hero Who Infiltrated Auschwitz is a biography of underground operative Witold Pilecki who accepted a mission to uncover the fate of thousands of people being interred at the concentration camp. While there, he managed to create an underground resistance army that smuggled evidence of Nazi atrocities out of Auschwitz via secret messages and radio broadcasts.

Fairweather, a former war reporter, used exclusive family papers and recently declassified files alongside unpublished accounts from the camp's fighters to tell the story of resistance. The biography had been the bookies' favourite to take home the prize on Tuesday night.

Chair of judges and broadcaster Sian Williams said the panel had been unanimous in their choice of Fairweather's "extraordinary story" following discussions that took several hours.

She explained: "One of the reasons that we loved it so much is it reads like a thriller, it doesn't really read like a biography at all and yet you don't feel as though it's over-dramatised in any way. The facts speak for themselves and they are incredibly well researched–about 3,000 different sources–and I think as a journalist that appealed to me, just how well researched it was."

Williams, whose own father-in-law was a Polish Jew who lost his family at Auschwitz, added: "This is a story that none of us had heard before and it just deserved to be shouted about."

On the timing of the win, she said: "We all felt that this was a book that stood out on its merits whenever it would have been published. It wasn't that we felt a particular way towards it because it's a prescient book for the moment. It didn't feel like that to us."

Accepting the award, Fairweather thanked his two researchers who joined him on the evening while dedicating the win to Pilecki's two children Andrzej and Zofia. He said: “In 1948 they sat in their school in communist Poland and listened on the school tannoy system as it was announced that their father had just been executed as a traitor and enemy of the state. For the next 50 years they had no idea what their dad had done in Auschwitz. Only with the fall of the Iron Curtain did his story start to emerge.

“It's been my absolute pleasure and great privilege of my writing to career to get to share his story with you. Thank you so much for taking him into your hearts. For me he's one of the great war heroes and I hope you all agree with me."

Ebury m.d. Joel Rickett said at least 20,000 more copies of the book would now be released, adding to the 50,000 paperbacks already in shops. He said: "I think it will now become a phenomenon, it will be a huge bestseller."

He went on: "It's an example of a long-term, deep creative commitment to an author and, I think publishing is pretty unique in this, where we invest in them and their talent and set them out on years of deep research.

"What his editor Jamie Joseph and the Ebury team has done is remarkable. It's a very complex story with research that needed to be done in a lot of difficult places. To get that done, to effectively research Pilecki's life and make it fresh and make it powerful is a remarkable achievement."

Film rights and the rights for a documentary following Fairweather have been signed and the book will become part of a trilogy "about people who fight against tyranny," his agent Clare Alexander said.

The book, currently number one in paperback non-fiction, won from a shortlist that featured First Novel Award-winner The Confessions of Frannie Langton by Sara Collins (Viking), Novel-winner Middle England by Jonathan Coe (Penguin), Poetry-winner Flèche by Mary Jean Chan (Faber), and Jasbinder Bilan’s Children’s Book-winning Asha & the Spirit Bird (Chicken House).

Alongside Williams, the other judges were comedian and author Ben Miller, actor Hugh Quarshie, broadcaster Anneka Rice, novelist John Boyne, author Clare Mackintosh, historian Professor Suzannah Lipscomb, critic Jade Cuttle and writer Bali Rai.

Also announced on the evening was the winner of the public vote for the Costa Short Story Award: Anna Dempsey for "The Dedicated Dancers of The Greater Oaks Retirement Community".