Elle Fanning as Mary Shelley

Douglas Booth as Percy Bysshe Shelley

Bel Powley as Claire Clairmont

Stephen Dillane as William Godwin

Joanne Froggatt as Mary Jane Clairmont

Tom Sturridge as Lord Byron

Ben Hardy as Dr. John Polidori

Maisie Williams as Isabel Baxter

Hugh O'Conor as Samuel Taylor Coleridge

Ciara Charteris as Harriet Shelley

Jack Hickey as Thomas Hogg

Laurence Foster as Bookseller

Derek Riddell as William Baxter

Stuart Graham as Publisher

Owen Richards as William Godwin

Martin Phillips as Deacon

Chloe Vos as Ianthe

Serena Barnes as Landlady

Mella Carron as Girl in Park

Sarah Lamesch as Eliza

Alexander Cobb as Scientist

Wilhelmina von Blumenthal as Servant of Byron

Nathan Vos as Young Percy