Sally Gardner was born and raised in London. She was thrown out of many schools, deemed unteachable, and put to a school for maladjusted children because she was dyslexic and did not learn to read or write until she was fourteen. Despite this, she graduated with honors from a prestigious London art college, received a scholarship to a theater school, and went on to work as a successful costume designer on a number of noteworthy performances. She began illustrating and eventually writing picture books and chapter books after the births of twin daughters and a son, frequently with fairytale or otherwise magical subject matter. The Sunday Times in London dubbed her an eccentric brilliance.

Her debut novel for older audiences is I, Coriander. Lucy Willow and the popular Magical Children series, The Strongest Girl in the World, The Invisible Boy, The Boy with Magic Numbers, The Smallest Girl in the World, The Boy with Lightning Feet, and The Boy Who Could Fly are just a few of her middle-grade novels. Her picture books include The Fairy Catalogue, The Glass Heart, The Book of Princesses, and Playtime Rhymes, which she wrote and drew.