Moseley was born in the Cotswolds village of Sheepscombe, Gloucestershire, England. He is the son of Juliette E. (née Fleming) and Peter A. Moseley, a cinematographer. Moseley is the eldest of three children; his siblings are Daisy Elizabeth Moseley (born 1989) and Benjamin Hugh Moseley (born 1992). Moseley attended Sheepscombe Primary School from September 1991 to July 1998, in which year he appeared as an un-named boy in Cider with Rosie. Moseley then continued his education at Wycliffe College. He took time off often at Downfield Sixth Form, Stroud (which is part of Marling School and its next door neighbour, Stroud High School), because he was filming The Chronicles of Narnia: The Lion, the Witch and the Wardrobe; however, he still achieved well and finished on time.