Born in Belfast, Lynch was the youngest of five children. He was interested in art from an early age, often choosing to spend his free periods during school in the art department. He recalls that Belfast in the 1970s was a "scary" place for a teenager, and he used drawing and reading as a "way of escaping for a while from the horrors that were happening around me in the real world." He attended the Brighton College of Art and departed in 1984 to begin working on children's books.