William Peter Moseley was born on April 27, 1987, in Gloucester, England, to Juliette (Fleming) and Peter Moseley, a cinematographer. He is the eldest of three children with a younger sister named Daisy and and younger brother named Ben. His father's name is also William's middle name.
He wanted to act since he was 10 years old. The young actor had a small role in Goodbye, Mr. Chips (2002) as Forrester, and he was cast as an extra in Cider with Rosie (1998). However, his big break came when he was cast in the part of Peter Pevensie in The Chronicles of Narnia: The Lion, the Witch and the Wardrobe (2005), picked out of thousands of boys for the role. He hopes he won't end up type-cast as Peter and to go on to carve a successful, well-rounded career in acting and directing in the future.
William completed Year 13 in 2006, with A Levels in Media Studies, English and Drama. In autumn 2006, he moved to New York for several weeks to study acting under Sheila Gray, where he trained at the famous Gleeson's gym in Brooklyn in preparation for filming The Chronicles of Narnia: Prince Caspian (2008).More