Born in Canada, Wallace moved to England in the 1960s. Her first published children's book was The Battle for Golddiggers Forest (1989). She went on to create several series characters, including Fearless Fiona and Flash Harriet, as well as the Crunchbone Castle Chronicles and the Lady Violet Winters mysteries for slightly older readers. She has also written children's books on historical figures (including Louis Pasteur and Thomas Edison) animals (Imagine You Are a Dolphin, etc.) and dinosaurs (I am a Diplodocus, etc.). Her children's novel Raspberries on the Yangtze was shortlisted for the Guardian Children's Fiction Prize in 2002.