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)

Ruth Cherrington

Swedish Queen (uncredited)

Ray Collins

Lecturer (voice) (uncredited)

Guy D'Ennery

Professor (uncredited)

George Davis

Cart Driver (uncredited)

William Edmunds

Cart Driver (uncredited)

Al Ferguson

Man at Accident (uncredited)

Edward Fielding

Board Member (uncredited)

Howard Freeman

Prof. Constant (voice) (uncredited)

Lisa Golm

Lucille (uncredited)

Ilka Grüning

Seamstress (uncredited)

Lumsden Hare

Professor Roget (uncredited)

Teddy Infuhr

Son (uncredited)

James Kirkwood

Board Member (uncredited)

Isabel La Mal

Woman at Accident (uncredited)

Gene Lockhart

Bit Part (uncredited)

Miles Mander

Businessman (uncredited)

George Meader

Singing Professor (uncredited)

Alan Napier

Dr. Bladh (uncredited)

Moroni Olsen

President of Businessman's Board (uncredited)

Gigi Perreau

Eve at 18 Months (uncredited)

Francis Pierlot

Monsieur Michaud (uncredited)

Almira Sessions

Madame Michaud (uncredited)

Arthur Shields

Businessman (uncredited)

Wyndham Standing

King Oscar (uncredited)

Ray Teal

Driver (uncredited)

Charles Trowbridge

Board Member (uncredited)

Michael Visaroff

Proud Papa (uncredited)

Marek Windheim

Jewelry Salesman (uncredited)

Frederick Worlock

Businessman (uncredited)

Eustace Wyatt

Doctor (uncredited)