Days Without End has been described as "compelling as it is moving"
Writer Sebastian Barry has become the first novelist to win the Costa Book of the Year award for the second time for his novel Days Without End.
Mr Barry (61) also won in 2008 with The Secret Scripture.
The Dublin-born author and playwright, who lives in County Wicklow with his wife and three children, was inspired to write about a gay relationship after his son came out.
Days Without End on teenager Thomas McNulty and his brother-in-arms John Cole, who fight in the Indian Wars and the Civil War.
Judges' chairman Professor Kate Williams said Mr Barry was the unanimous choice for his "searing, magnificent and incredibly moving description of how the West was won".
Mr Barry takes home another £30,000 (€35,000) for scooping the overall prize and being named as Book of the Year award winner.
Professor Williams said of the winning book: "It is very striking we are thinking and looking so much about American history and life at the moment and here is this book about the founding of America."
She said the book touches on "how power corrupts, what power does to you" and also on whether "it is possible to have power over others and still retain your humanity".
Previous winners of the award include poets Seamus Heaney and Ted Hughes.
Speaking immediately after the announcement, Arts Council Chair, Sheila Pratschke said, "Sebastian Barry is a writer of tremendous talent. Days Without End is as compelling as it is moving, as lyrical as it is inventive. Barry's commitment to the craft of writing has long been recognised in Ireland and abroad, and it is a thrill to see his latest novel win such acclaim."
She continued: "The Arts Council was also delighted to see Irish writers Jess Kidd and Billy O'Callaghan taking first and second place in the Costa Short Story Competition, and Irish-based author Brian Conaghan winning the 2016 Costa Children's Book Award. All further proof, as if it were needed, of the wealth of contemporary Irish writing talent. It's a wonderfully exciting time for literature in Ireland."