Margaret Mahy ONZ (born in Whakatane, New Zealand on 21 March 1936) is a well-known New Zealand author of children's and young adult books. While the plots of many of her books have strong supernatural elements, her writing concentrates on the themes of human relationships and growing up.

Her books The Haunting and A Supernatural Romance both received the Carnegie Medal of the British Library Association. She has written more than 100 picture books, 40 novels and 20 collections of short stories. Among her children's books, A Lion in the Meadow and The Seven Chinese Brothers and The Man Whose Mother was a Pirate are considered national classics. Her novels have been translated into German, French, Spanish, Dutch, Norwegian, Danish, Swedish, Finnish, Italian, Japanese, Catalan and Afrikaans. In addition, some stories have been translated into Russian, Chinese and Icelandic.

For her contributions to children's literature she has been made a member of the Order of New Zealand. The Margaret Mahy Medal Award was established by the New Zealand Children's Book Foundation in 1991 to provide recognition of excellence in children's literature, publishing and literacy in New Zealand. In 2006 she was awarded the Hans Christian Andersen Award (known as the Little Nobel Prize) in recognition of a "lasting contribution to children's literature". In March 2009, Mahy was commemorated as one of the Twelve Local Heroes, and a bronze bust of her was unveiled outside the Christchurch Arts Centre.

In 2010 a television series of her book Kaitangata Twitch aired on Maori Television. Directed by Yvonne Mackay and produced by The Production Shed.TV, the series includes a cameo appearance by Margaret Mahy in a library scene.

Margaret Mahy currently resides on Banks Peninsula, Canterbury, in the South Island of New Zealand.