Stuart Blackburn was presented the award at the HNS Conference in Oxford for his novel "Into the Hidden Valley".
The book, published by Speaking Tiger, looks into a little-known episode in the colonial history of British India.
Blackburn vividly brings alive the world of the Apatanis.
His exploration of what happens when this settled civilisation forcibly collides with British Empire sensitively portrays the impact of the forces of colonialism on both sides.
"Into the Hidden Valley" was chosen for the award ahead of Helena Page Schrader's "Defender of Jerusalem" and "Allegiance" by Kermit Roosevelt.
The award is named in memory of writer-historian Bennetts who was a specialist in early 19th century British history and the Napoleonic wars.
Blackburn says he first became interested in the Tibeto-Burman-speaking tribes of northeast India when he went to Arunachal Pradesh in 1999.
"I spent a large part of the next decade researching the cultures and oral traditions of one particular group, the Apatanis, who live in the 'hidden valley' of the story. Two of my monographs document their storytelling arts."
US-born Blackburn spent two and a half years in the rice fields and villages of south India, where he learned to speak Tamil.
He is the author or editor of 16 books on Indian culture and folklore, mainly in south India (where his first novel "Murder in Melur" is set) and northeast India.
One book, a study of shadow puppet theatre in Kerala, won the runner-up prize for the UK Folklore Book of the Year, while a translation of an early Tamil novel won the AK Ramanujan Prize in the US.
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