Margaret Mahy was born and raised in Whakatane and began writing children's books in earnest at the age of eighteen. After graduating with a Bachelor of Arts in 1955, Margaret trained as a librarian and in 1967 began work at the School Library Service in Christchurch. During this time she had stories published in the New Zealand School Journal, however her big break came in 1968 when an American publisher found the text of A Lion in the Meadowand bought it – along with all the other work Margaret had produced over the years. Consequently, eight books were published simultaneously.
Margaret became a full-time writer in 1980. Her novel The Haunting won the Carnegie Medal of the British Library Association – the first writer outside the United Kingdom to do so. Margaret's work has been translated into fifteen languages and won the Carnegie Medal three times (1982, 1986 and 1987); the Young Observer Fiction Prize (1986); the Italian Premier Grafico Award (1976) and the Dutch Silver Pencil Award (1977). She has also been awarded the Esther Glen Medal of the New Zealand Library Association six times, the first in 1970 for The Lion In The Meadow.
Margaret has been appointed a writing fellow in New Zealand, Australia, and in the United States. Her works have won awards and been included in prestige listings by journal editors, librarians and educationalists. The Australian animated television show The Magical World of Margaret Mahy is based on Margaret's children's stories. In 1999, A Summery Saturday Morning won Best Picture Book at the New Zealand Post Children's Book Awards, and 24 Hours received an Honour Award at the 2001 New Zealand Post Children's Book Awards. Alchemy (2002) was shortlisted for the 2003 LIANZA Esther Glen Medal and won the Best Senior Fiction at the New Zealand Post Children's Book Awards 2003.
In 2005 Harper Collins published Margaret Mahy: A Writer's Life by Tessa Duder. In the same year, Margaret was awarded the $60,000 Prime Minister's Award for Literary Achievement and was awarded an Arts Foundation Icon Award.
Her books Maddigan's Fantasia (HarperCollins, 2005) (Junior Fiction section), and Kaitangata Twitch (Allen & Unwin 2005) (Young Adult section) were nominated in the 2006 New Zealand Post Book Awards for Children and Young Adults. 2006. Kaitangata Twitch won the Honour Award in the Young Adult section. In the same year Margaret was announced as the winner of the world's premier prize for children's writing, the Hans Christian Andersen Award. Often called the "Little Nobel", the award is given biennially by the International Board on Books for Young People (IBBY) to honour an author who has madea lasting contribution to international children's literature.
In 2008 Margaret was nominated as one of two New Zealand candidates (with Joy Cowley), out of an international total of 153, for the 540,000 EURO Astrid Lindgren Memorial Award 2009 for children's literature.
Margaret won the 2011 NZ Post Children's Book Awards with The Moon and Farmer McPhee - illustrated by David Elliott. The book also won the Best Picture Book Award
In 2016, it was announced that Mahy's best selling Young Adult novel The Changeover is being made into a movie, which will be presented to potential buyers at that year's Cannes market.
Margaret passed away at the age of 76 on 23 July 2012.