Gwen was brought up in Wales. Originally she had her heart set on becoming a naturalist as she loved studying insects and drawing them. Her trips abroad when she was young are associated with finding new and strange looking creatures! After school she migrated north to Edinburgh to study art where she graduated with a First in illustration and was awarded the Helen A. Rose Bequest for art.

Gwen's first picture book, Guess What I Found In Dragon Wood (text by Tim Knapman) was published by Puffin, as was The Bog Baby by Jeanne Willis, and a collaboration with Jenny Nimmo, The Beasties, by Egmont. She has since published many more, including two about Bear and Bird that she has written herself. Gwen has illustrated Stories from Bug Garden (Candlewick), Tiger Lily, which she wrote and illustrated, and Flat Cat, written by Hiawyn Oram.
Gwen is also the illustrator for the Charmseekers series by Amy Tree, published by Orion. She lives in Bristol with her young sons.