Duddle studied illustration at college. Starting his career in illustration as a freelance artist, he began designing characters for computer games. He wrote a picture book called 'The Pirate Cruncher' that was published in 2009 which was followed by 'The Pirates Next Door' which won the 2012 Waterstones Children's Book Prize.
Duddle then tried writing sci-fi with 'The King of Space' and then 'Gigantosaurus'.
In 2014, Bloomsbury decided it was time to recreate the covers of the Harry Potter books. Ten years before, Rowling was impressed by an illustration he made for a character in one of the Pirates of the Carribbean game. They approached him to create a test cover along with three other illustrators.
Duddle was picked as he was the only one to make a cover where Harry is facing the reader. Duddle was worried before he made the cover as he thought he wouldn't do well. He took the commission very seriously and read and watched every single Harry Potter book and film in eight months.