Jessica Ellen Cornish was born in London,[2] to Rose (née Archer) and Stephen Cornish. She was educated at Mayfield High School in the London Borough of Redbridge. She attended Colin's Performing Arts School and as an 11-year-old she was cast in Andrew Lloyd Webber's West End production of Whistle Down the Wind.[9][10][11] She subsequently joined the National Youth Music Theatre and appeared in their 2002 production of The Late Sleepers.