While at school, Dormer trained in dance at the Allenova School of Dancing. She says she was the "academic hopeful" of the family and was provisionally offered a place to study history at the University of Cambridge; but, in her A-level History exam, she did not achieve the A grade she needed having misread a question. Dormer chose to audition for drama schools, training at the Webber Douglas Academy of Dramatic Art in London. Her first professional acting role was in "The Comedy of Errors" in 2003.