Irish writer Sebastian Barry on Tuesday became the first novelist to scoop the Costa Book of the Year award twice, with his portrayal of an 1850s gay relationship between US soldiers.

"Days Without End" was the judges' unanimous choice for Barry's "searing, magnificent and incredibly moving description of how the West was won", said the award chair Kate Williams.

The novel follows the relationship of two young men fighting for the US army, as they journey from Wyoming to Tennessee.

Collecting his £30,000 ($38,000, 35,000 euros) prize at a ceremony in London, Barry said he was thrilled with the win.

"You have made me crazy happy from the top of my head to my toes in a way that is a little bit improper at 61," said the author.

Barry previously won the Costa Book of the Year award in 2008 for his novel "The Secret Scripture".

While he is the first novelist to take the prize on two occasions, poets Seamus Heaney and Ted Hughes have each won twice.

Williams praised the "beautiful characterisations and brilliant writing" of this year's winner, explaining Barry chose to write about the same-sex relationship between the two soldiers after the author's son came out as gay.

The award is open to authors living in Britain and Ireland and attracted 596 entries for the 2017 prize, five of which were shortlisted.

Last year the award was picked up by Frances Hardinge for "The Lie Tree", a 19th-century detective novel.