At age 12, Leonore relocated to Los Angeles with her mother and sister, where she finished high school and studied music.

In January 1920, inventor and radio pioneer Lee DeForest brought her to the cramped studio of his station, 2XG, located in New York City's World's Tower, where De Leath broadcast "Swanee River".

Although not, as is sometimes stated, the first broadcast of live singing,[3] she established herself as a skilled radio performer, and De Forest would later note: "She was an instant success.

[4] According to some historical accounts of this incident, having been advised that high notes sung in her natural soprano might shatter the fragile vacuum tubes of her carbon microphone's amplifier, De Leath switched to a deep contralto and in the process invented "crooning",[5] which became the dominant pop vocal styling for the next three decades.

By 1921, in the formative years of commercial radio, De Leath began singing at WJZ, in Newark, New Jersey (a station later known as WABC in New York City).

[6] These included Gloria Geer, Mamie Lee, Sadie Green, Betty Brown, Nancy Foster, Marion Ross, Glory Clarke, Angelina Marco, and Gertrude Dwyer.

[1] De Leath had a highly versatile range of styles, and as material required could adapt as a serious balladeer, playful girl, vampish coquette, or vaudeville comedian.

After her career went into decline, De Leath endured considerable financial difficulties, complicated by a drinking problem, which contributed to her death at age 48 in Buffalo, New York.