"I honestly didn't know if I'd win either award. There was some stiff competition in both categories.
"The award ceremony was quite nerve-wracking and for a second I couldn't believe it when they opened the award envelope and read my name out. It was one of those moments when the world seems to be in slow motion," Mr Ward said.
He also said Storylines is a wonderful organisation that champions great New Zealand writing for children - making it "special for The Traitor and the Thief to be a notable book of 2018".
The Traitor and the Thief is aimed at 10 to 15-year-olds and is set in a Victorian England heavily influenced by steampunk.
The plot concerns Sin, a 14-year-old orphan who, caught stealing a priceless necklace, is offered redemption if he joins a secret spy organisation. Sin is the thief of the title - as for the identity of the traitor - it's up to Sin and his mates to unmask the villain.
A sequel to The Traitor and the Thief has already been written and Ward hopes to have it published later this year.
He is also finishing the final draft of the first book in a new series which he would love to see in print in 2019.
He has written three previous novels, that "weren't good enough to be published" but he thinks of them as his "apprenticeship".
"One of the biggest surprises for me is the number of adults that have thoroughly enjoyed The Traitor and the Thief. I knew it was a great children's book but it seems to have really struck a chord with adults too, and that's fantastic," Mr Ward said.