Wellingtonian De Goldi, 49, won for her novel The 10PM Question, the tale of Frankie Parsons and his eccentric family and friends.
She wooed the judging panel, just as she had captured the hearts of the young readers who had kept the book on the bestseller lists for months.
Convenor of judges Bill Nagelkerke said The 10PM Question had a rare quality.
"De Goldi's winning book invites you to become part of another family, to spend some quality time with its members, become engrossed in the family dynamics to the point that, when it's time to leave, we very reluctantly shut the door on these new friends because we don't wish to part from them, because this family has now become our family, too," he said.
The 10PM Question also took the young adult fiction category at a gala ceremony held in the Auckland Museum this evening.
De Goldi was awarded $7500 for each of her wins.
The judging panel applauded the authors, illustrators and publishers for striving for stories that stimulated, excited, took risks and inspired.
"We recognise stalwart veterans of the art and craft of writing and illustrating and celebrate the emergence of new voices whose words and images will ensure that writing for children and young adults in this country remains in fine shape for the foreseeable future."
Category winners and the honour award recipient were:
Picture Book: Roadworks written by Sally Sutton and illustrated by Brian Lovelock.
Honour Award: Piggity-Wiggity Jiggity Jig written by Diana Neild and illustrated by Philip Webb.
Non-fiction: Back & Beyond: New Zealand Painting for the Young & Curious by Gregory O'Brien.
Junior Fiction: Old Drumble by Jack Lasenby.
Best First Book Award: Violence 101 by Denis Wright.
Young Adult Fiction and New Zealand Post Book of the Year: The 10PM Question by Kate De Goldi.
Children's Choice Award: The Were-Nana written by Melinda Szymanik and illustrated by Sarah Nelisiwe Anderson.
The winner of each category was awarded $7500, with the winner of book of the year taking home an extra $7500.
The winner of the best first book and the children's choice award received $2000 each.
The honour award recipient received a monetary award of $500.
