[6] Niesen debuted on radio on a small station when she was 15 years old, having roles in works by Ibsen and Shakespeare.

In his book, Historical Dictionary of American Radio Soap Operas, Jim Cox wrote: "Mary Noble's alter ego, Niesen, consistently projected the appealing inflections required by the role: invariably soft-spoken, tenderhearted, and forgiving.

Her empathetic expressions contributed to winning the part and helping her keep it for the final 14 years the serial was on the air (1945–59).

"[10] Other programs in which Niesen was heard included Life Can Be Beautiful, The Right to Happiness,[1] Light of the World, Meet Miss Julia, Into the Light, The Man I Married, We, the People, March of Time and Manhattan at Midnight.

[12] Niesen married the actor Melville Ruick on March 11, 1949, in New York City.