Mickey Rooney as Thomas Alva 'Tom' Edison

George Bancroft as Samuel 'Sam' Edison

Fay Bainter as Mrs. Samuel 'Nancy' Edison

Virginia Weidler as Tannie Edison

Eugene Pallette as Mr. Nelson

Victor Kilian as Mr. Dingle

Bobby Jordan as Joe 'Joey' Dingle

Lloyd Corrigan as Dr. Pender

John Kellogg as Bill Edison

Clem Bevans as Mr. Waddell

Eily Malyon as Miss Lavina Howard, School Teacher

Harry Shannon as Army Captain Brackett

Ernie Adams as Passenger Buying Maple Sugar

Maude Allen as Woman Fainting at Downed Bridge

Jessie Arnold as Woman at Station

Polly Bailey as Woman at Station

Sherwood Bailey as Red, Joe's Friend

Jack Baxley as Man at Dingle's Store

John Beck as Bartender

Arthur Belasco as Telegrapher

Sammy Blum as Train Passenger

Stanley Blystone as Army Officer on Train

Wade Boteler as Si Weaver

Eddy Chandler as Mr. Briggs

Jack Daley as Man at Station

Leigh De Lacey as Train Passenger

John Webb Dillion as Man at Station

Fern Emmett as Mrs. McCarney

Budd Fine as Train Passenger

Olin Howland as Telegrapher (Indian Attack)

Philip Hurlic as Black Boy at Tree

John Ince as Man at Station

Mitchell Ingraham as Man at Station

Milton Kibbee as Baggage Man

Del Lawrence as Train Passenger

Mitchell Lewis as McGuire - Train Engineer

George Magrill as Train Passenger

Wally Maher as Man at Station

Claire McDowell as Woman at Station

Frances Morris as Woman at Station

Emory Parnell as Bob

Lee Phelps as Train Engineer Miller

Victor Potel as Mr. Tompkins

Mickey Rentschler as Johnny, Joe's Friend

Marion Sheldon as Train Passenger

Buster Slaven as Boy at Tree

Marvin Stephens as Frank Allen

Harry Strang as Army Officer

Forrest Taylor as Train Passenger

Spencer Tracy as Man Admiring Portrait of Thomas A. Edison

Frank Whitbeck as Narrator (voice)

Joe Whitehead as Mr. Hodge

Al Thompson as Man at Station

J.M. Kerrigan as Mr. McCarney