The judges' decision was unanimous and they only 'took an hour to decide'.
Douglas Stuart was born and raised in Glasgow. After graduating from MA Fashion Menswear at the RCA in 2000, he moved to New York, where he began a career in design.
Shuggie Bain is his debut novel. It follows the life of Agnes Bain, who is descending into despair and struggling with alcohol after the breakdown of her marriage.
All but one of her children have been driven away by her deterioration, and that child, Shuggie, struggles to help Agnes while suffering huge personal problems of his own.
Stuart said he was 'absolutely stunned' to win and added he would like to give his fellow nominees 'a hug' and that the 'greatest gift' was being able to "touch readers' lives".
Chair of judges Margaret Busby said that the book is ‘challenging, intimate and gripping... anyone who reads it will never feel the same’.
The novel is 'destined to be a classic' and is 'full of such emotional rage, a book that can make you laugh as well as make you cry', Busby said.
'It's dealing with tough subject matter, with characters not having an easy time - some of the things that happen will make you smile but it's not one where everyone lives happily ever after.
“It's not a pleasant read, but it's a hopeful read, challenging, intimate, gripping.”
Stuart has said the book changed his life because it was one of the first times he had seen his people and dialect on the page.
Stuart’s short stories have appeared in The New Yorker and his essay on Gender, Anxiety and Class was published by Lit Hub. He is currently at work on his next book.