Thomas was born in Norwich but grew up in Wales and lived for many years in France. He is the author of the acclaimed and multi-award-winning Eerie-on-Sea series, starting with Malamander, which has been translated into twenty languages and has sold more than half a million copies worldwide. Thomas has also written and illustrated a number of picture books, and collaborated as illustrator with author Marcus Sedgwick on the graphic novel Scarlett Hart: Monster Hunter. Thomas's first professional illustration commission - after graduating from Norwich School of Art - was the cover art for Harry Potter and the Philosopher's Stone by J.K. Rowling.