Gadsby was born in Derbyshire, England, and went to school in Invercargill when his family moved to New Zealand.
Gadsby appeared in numerous television programmes, several films, and wrote more than 20 books, mainly for children.
He wrote for The New Zealand Herald, Metro and The Listener, and performed corporate voicing.
[4] In 2011, he was convicted of his fourth drink-driving charge, having been stopped with a breath alcohol reading 2.5 times in excess of the legal limit.
[11] Gadsby, David McPhail and A. K. Grant, were named best writers at the 1996 Film and Television Awards, for the series Letter to Blanchy.