Hardwicke was born in London, England, to actors Sir Cedric Hardwicke and Helena Pickard. He started his film career in Hollywood at 10. He was in Victor Fleming's film "A Guy Named Joe" with Spencer Tracy. He went back to England, attended Stowe School, and did his military service in the Royal Air Force. He then joined the Royal Academy of Dramatic Art (RADA) to learn to be an actor.