Greer Garson

Marie Curie

Walter Pidgeon

Pierre Curie

Henry Travers

Eugene Curie

Albert Bassermann

Professor Jean Perot

Robert Walker

David Le Gros

C. Aubrey Smith

Lord Kelvin

May Whitty

Madame Eugene Curie

Victor Francen

President of University

Elsa Bassermann

Madame Perot

Reginald Owen

Dr. Becquerel

Van Johnson

Reporter

Margaret O'Brien

Irene Curie - Age 5

James Hilton

Narration Spoken By (voice)

Mariska Aldrich

Tall Woman (uncredited)

Tony Carson

Man at Accident (uncredited)

Mervyn LeRoy