Her father was a successful criminal defense attorney who had defended infamous gangsters Bonnie and Clyde, Baby Face Nelson and Pretty Boy Floyd. After her parents marriage dissolved, her mother took her to Hollywood where she took Tap lessons and started her career as a Professional child Tap Dancer at age seven to help support her mother. Later, she made her movie debut in "Anne of Green Gables" in 1934 at age fifteen, also appearing in "The Good Fairy" (1935) and "Devil on Horseback" (1936) before signing with RKO in 1937.

        Many records show her birth date as 1919, however this was made up so she would be the legal age of eighteen to fulfill her movie contract. Miller had a vigorous tap-dancing style, great legs and a winning personality which was far better than her actual acting ability, but her talents made up for it.

        Her inventive style of Tap in the MGM musicals had her whirling her fabulous legs around a floor which offered Miller frequent opportunities to strut her stuff, sway, swirl, and clackety-clack in flashy, brilliantly choreographed dance routines. She is said to be the fastest female tap dancer with 500 taps a minute. At one point in her career she insured her Legs for a Million dollars and was known as the "Lady with the Million Dollar Legs."