She was born in 1920 in Glenties, County Donegal, Ireland as Mary Margaret Kiely.

She was married to Irish actor Cyril Cusack and they had five children Sinéad, Sorcha, Niamh, Paul and Pádraig.

Her grandsons are actors Max Irons and Calam Lynch, and the politician Richard Boyd Barrett.

[3] In 1946 she appeared in a Radio Eireann production of a play by Irish playwright Teresa Deevy called Katie Roche[4] and again in 1947 in Wife to James Whelan,[5] these were both produced by Gabriel Fallon.

She is best known for her roles in Odd Man Out (1947), The Rising of the Moon (1957), Von Richthofen and Brown (1971), also The Loves of Cass Maguire (1975), and Playboy of the Western World (1946).