Greer Garson (Mme. Marie Curie)
Walter Pidgeon (Pierre Curie)
Robert Walker (David LeGros)
Van Johnson (Reporter)
Albert Basserman (Prof. Jean Perot)
Margaret O'Brien (Irene at Age Five)
Henry Travers (Eugene Curie)
Eustace Wyatt (Doctor)
Ruth Cherrington (Swedish Queen)
Frederic Worlock (Businessman)
Michael Visaroff (Proud Papa)
Charles Trowbridge (Board Member)
Ray Teal (Driver)
Wyndham Standing (King Oscar)
Ray Collins (Lecturer)
James Hilton (Narrator)
Mariska Aldrich (Tall Woman)
Harold de Becker
Tony Carson
Nestor Eristoff (Board Member)
Nita Pike (People at Accident)
George Davis
Howard Freeman (Prof. Constant)
Marek Windheim (Jewelry Salesman)
Arthur Shields (Businessman)
James Kirkwood
Teddy Infur (Son)
Lumsden Hare (Prof. Roget)
Lisa Golm (Lucille)
Dorothy Gilmore (Nurse)
Victor Francen (President of University)
Edward Fielding
Al Ferguson
William Edmunds (Cart Driver)
Guy D'Ennery (Professor)
Gene Lockhart
Miles Mander (Businessman)
Almira Sessions (Mme. Michaud)
Francis Pierlot (M. Michaud)
Gigi Perreau (Eva at Age 18 Months)
Isabelle Lamore
Moroni Olsen (President of Businessmen's Board)
Alan Napier (Dr. Bladh)
Leo Mostovoy (Photographer)
George Meader (Singing Professor)
Reginald Owen (Dr. Becquerel)
C. Aubrey Smith (Lord Kelvin)
Dame May Whitty (Mme. Eugene Curie)
Elsa Basserman (Madame Perot)