Richard Osman has been crowned author of the year at the British Book Awards after the runaway success of his debut novel The Thursday Murder Club.
Pointless star Osman said his win for his story of elderly amateur sleuths was an "absolute dream come true".
Also triumphant was Douglas Stuart's hard-hitting debut Shuggie Bain, which won the overall book of year, following 2020's Booker Prize-winning success.
Judges called Stuart's book, which also won best debut fiction, "exceptional".
The Thursday Murder Club follows a group of residents in a retirement village, whose hobby is trying to solve cold-case crimes, until suddenly they find themselves caught up in a murder mystery of their own.
The novel went straight to number one in the charts when it was released in September and has been in the top 10 fiction hardbacks ever since.
It is now only the second adult hardback fiction novel, after The Lost Symbol by Dan Brown, to sell more than one million copies in the UK this century.
Two more instalments have been commissioned and Steven Spielberg has bought the film rights, with Osman acting as an executive producer.
Osman told BBC News: "I am genuinely thrilled that people have loved The Thursday Murder Club, and this award is the cherry on the cake. Speaking of which, last time I was up for an award, Pointless lost out to Extreme Cake Makers, so this makes a very nice change."
Alice O'Keeffe, chair of the panel of industry expert judges, said the success of Osman's book was "extraordinary".
"The Thursday Murder Club now holds the record for the longest consecutive run at the top (16 weeks), and it is by far the fastest-selling crime debut of all time.
"This success established TV producer and Pointless star Richard Osman as a mega-brand author straight out of the gate, making him a natural choice for the British Book Awards author of the year."
The book of the year is chosen from the winners in nine categories: fiction, debut fiction, children's fiction, non-fiction narrative, pageturner, lifestyle, crime fiction-thriller, children's illustrated and non-fiction plus audiobook.
Stuart's overall winning debut novel, about a boy growing up amid poverty and addiction in 1980s Glasgow, beat off competition from books by established authors such as Maggie O'Farrell's Hamnet and David Olusoga's non-fiction Black and British.
Stuart said of his success: "To everybody who embraced the story and - especially in such a tough and weird year - has kept literature at the heart of our communities, I'm so grateful for you."
Book of the year judge Ella Risbridger added: "As a testament to the ways poverty, addiction and violence scar themselves on the body and the mind, Shuggie Bain remains unsettlingly timely.
"I hope in years to come, we can read it purely as a period piece; purely as a reminder of how things used to be - but for now we must read it also as something of an incentive and an invitation to change."
Other winners at the awards, which were held virtually on Thursday, included Maggie O'Farrell for her best-selling novel Hamnet.
The book, which won best fiction book (non-debut) and was inspired by the true story of William Shakespeare and Anne Hathaway's only son, has previously won the Women's Prize for Fiction. Troubled Blood by Robert Galbraith, also known as JK Rowling, won the crime and thriller fiction category.
Children's fiction book of the year went to The Highland Falcon Thief, by MG Leonard and Sam Sedgman. The award for best non-fiction, illustrated children's book went to David Olusoga's essential Black and British.
Charlie Mackesy, author of The Boy, the Mole, the Fox and the Horse, was named illustrator of the year.
Winners in full:
- Book of the year: Shuggie Bain by Douglas Stuart
- Author of the year: Richard Osman
- Fiction: Hamnet by Maggie O'Farrell
- Fiction: debut: Shuggie Bain by Douglas Stuart
- Fiction: crime & thriller: Troubled Blood by Robert Galbraith
- Children's fiction: The Highland Falcon Thief, by MG Leonard and Sam Sedgman,
- Children's illustrated & non-fiction: David Olusoga' Black and British
- Non-fiction: lifestyle: - Skincare by Caroline Hirons
- Non-fiction: narrative: Diary of a Young Naturalist by Dara McAnulty
- Pageturner: Where the Crawdads Sing by Delia Owens
- Audiobook: Think Like A Monk by Jay Shetty
- Illustrator of the year: Charlie Mackesy