A Kind Of Spark, which also won the 2021 Blue Peter Prize for best story, tells the story of 11-year-old Addie, who is autistic, as she campaigns for a memorial in memory of the witch trials that took place in her Scottish home town.
The story was born from McNicoll’s own experience of neurodiversity and her desire to see greater representation in children’s books.
She said: “Winning the WCBP21 is completely staggering. I will never say ‘I can’t’ again.
“To know that booksellers chose A Kind Of Spark, out of an incredible shortlist like this, it is the highlight of my debut.
“I’m so grateful to Waterstones for their support and I’m proud and extremely emotional to see Addie join past winners.”
The book was named both overall winner and winner of the younger readers category.
Special copies of the book, featuring a letter by the author to her younger self and the first chapter from McNicoll’s second book Show Us Who You Are, will be available at Waterstones.
Waterstones children’s buyer Florentyna Martin said: “We have fallen in love with Addie, whose courage and determination are a guiding light, often reminding the world that kindness must prevail wherever we go.
“Elle McNicoll is undoubtedly an outstanding new talent in children’s books and will inspire readers young and old for generations to come.”