The Dublin-born author was announced the winner last night for his brilliant historical novel, 'Days Without End'. He also won the same award - which was previously known as the Whitbread Book Award, which was set-up to honour Irish and British authors - back in 2008 for his critically acclaimed novel, 'The Secret Scripture'.
It was a great night for Irish writers, with 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.
Accepting the main award last night, Sebastian Barry said: "You nearly had the first instance of a posthumous winner - I got such a fright!
"It's often said about the shortlists of prizes that any of them could have won, and I think the judges would agree on this occasion that any of these amazing, amazing books could have won - leaving aside my own!"
On the night, Barry was competing against authors Francis Spufford, Keggie Carew, Brian Conaghan, and Alice Oswald.
He added, "I do want to thank the judges; you've made me 'crazy happy' from the top of my head to my toes in a way that is a little bit improper at 61!"
Sebastian Barry's latest novel was described by the award's judges as "a miracle of a book – both epic and intimate – that manages to create spaces for love and safety in the noise and chaos of history."
After the award ceremony, Sebastian Barry told the BBC: "I was completely gobsmacked, if you're familiar with that good Irish word! There's a word I tried to get back into usage in the book which means 'the bee's knees' and it's the 'sockdolager'. That was the sockdolager of amazing outcomes, I have to say."
He also revealed that he was inspired to write the book after his own son came out. "My beautiful and incredible son Toby, who came out when he was 16 in Ireland - in a rural part of Ireland - and has spent the last few years giving me a university training in what it means to be gay and has opened my eyes to this wondrous condition of being.
"I thought in the book if I could go back to a time in America, despite the great maelstrom of the nation being born... If I could find this place where a man could love another lad and not be bothered with it by other people, and just have their lives and progress in their lives, then I was making a little secret prayer in the future where somebody as immaculate as my boy would never have to be bothered by prejudice or the comments of the ignorant. Because I did conclude it was a magnificent state of being. So in the book I'm trying to describe their love in a sort of unremarkable way, because it's a normal and natural part of being a human creature."
He jokingly said that his son had taken "ages" to read the novel. Laughing, he added: "None of my children read my books! They just want me to be 'Stupid Old Dad', driving them 'round like a taxi man and buying them shoes when they need them!
"And I understand all that but I did feel he should read it; he did read it and he said quietly to me a couple of months ago, 'Dad two things: first, you're not gay, but you're an ally'. And then he said, 'And I like your book'. Those three words [sic] were precious and wonderful to me."

The Arts Council has congratulated the Wicklow-based author on his historic win, which includes a cash prize of £30,000. "Sebastian Barry is a writer of tremendous talent. Days Without End is as compelling as it is moving, as lyrical as it is inventive," commented the Arts Council Chairperson, Sheila Pratschke. “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.”
The Arts Council said it was also delighted that other Irish writers had done exceptionally well on the night too. "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," added Sheila Pratschke.