A graduate of New York's Professional Childrens' School, Helen Mack appeared as a child actress in such Broadway productions as The Dybbuk and such films as Gloria Swanson's Zaza (1923); during this period, she was sometimes billed as Helen Macks. Her first adult role was in D.W. Griffith's last film, 1931's The Struggle. Signed to a Fox contract in 1932, Mack moved to RKO a year later, where she was leading lady in two Merian C. Cooper efforts, Son of Kong (1933) and She (1935). Free-lancing throughout the 1930s, Mack played such roles as Harold Lloyd's pugnacious sister in The Milky Way (1936) and hard-bitten "shady lady" Mollie Malloy in His Girl Friday (1939). In 1941, Mack launched her radio career when she replaced the late Donna Damerel on the popular radio serial Myrt and Marge. Three years later, Mack became a radio producer/director, responsible for such series as A Date with Judy and Beulah. Helen Mack also authored one stage play (under her married name Helen McAvity), the 1965 flop The Mating Dance.