James Purefoy as Thomas Marshall

Kate Mara as Lady Isabel

Jason Flemyng as Becket

Paul Giamatti as King John

Brian Cox as Albany

Derek Jacobi as Cornhill

Charles Dance as Stephen Langton, Archbishop of Canterbury

Aneurin Barnard as Guy

Jamie Foreman as Coteral

Mackenzie Crook as Marks

Rhys Parry Jones as Wulfstan

Vladimir Kulich as Tiberius

David Melville as Baron Darnay

Annabelle Apsion as Maddy

Steffan Rhodri as Cooper

Daniel O'Meara as Phipps

Bree Condon as Agnes

Guy Siner as Oaks

Marcus Hoyland as Abbott Marcus

John Pierce Jones as Cook

Jeff Jones as Head Clerk

Ceri Mears as Blacksmith

Kenneth Collard as Sapper Captain

Wyn Bowen Harries as Baron

Dewi Williams as Baron

John Weldon as Castle Darney Sentry

Laura Sibbick as Castle Servant Girl

Edward Manning as Mercenary

Simon Nader as Hungarian Mercenaries (voice)

Steve Purbrick as Tavern Landlord

Peter Bartfay as Hungarian Mercenaries (voice) (uncredited)

Dan Burman as Mercenary Scout (uncredited)

Ian M. Court as Priest (uncredited)

David Harkus as Young Soldier (uncredited)

Gerald Royston Horler as Hungarian Warrior (uncredited)

Rhys Horler as Hungarian Warrior (uncredited)

Rhi Louise as Topless Wench (uncredited)

Stuart Mager as Garrison Guard (uncredited)

Christian Morgan as Wounded Guard (uncredited)

Stevie Raine as Mercenary Fight Performer (uncredited)

Carlton Venn as King's Aid 2 (uncredited)