She was selected to star in Korda's 1937 film, I, Claudius, as Messalina, but her injuries in a car accident resulted in the film being abandoned. She went on to appear as Cathy in the highly acclaimed film Wuthering Heights (opposite Laurence Olivier; 1939), as George Sand in A Song to Remember (1945) and as the Empress Josephine in Désirée (1954).
Oberon's mother, Charlotte Selby, who was actually her birth grandmother, died in 1937. (Merle's biological mother was Charlotte's daughter, Constance, who was 12 years old when Merle was born.) In 1949, Oberon commissioned paintings of Charlotte from an old photograph, which hung in all her homes until Oberon's own death in 1979.