[5] Born to an English mother and Irish father in South Africa and raised in County Tipperary, Cusack dropped out of law school to join the Abbey Theatre and remained with the company for 13 years, acting in over 60 plays.

His mother, Alice Violet (née Cole), was an English Cockney actress and chorus girl, and his father, James Walter Cusack, was an Irish mounted policeman in Natal Colony, South Africa.

[9] Cusack's favorite roles included The Covery in The Plough and the Stars and Christy Mahon in The Playboy of the Western World, which he reprised numerous times.

His breakthrough role was as a wiry IRA getaway driver opposite James Mason in Carol Reed's Odd Man Out (1947).

Cusack returned to Italy several times throughout his career, particularly in the 1970s, both acting on-camera and working as a voice artist, helping create English-language dubs of Italian films.

"[12] His religious credentials came under scrutiny following his death and the revelation that he had been unfaithful in his first marriage, with a long-term mistress, Mary Rose Cunningham, who bore him a daughter, Catherine.

Cusack was a longtime friend of Irish attorney general, Chief Justice and President of Ireland Cearbhall Ó Dálaigh, whom he got to know when they were students at University College Dublin in the early 1930s.

[14] Cusack is the maternal grandfather of Irish Socialist Workers Party TD Richard Boyd Barrett and English actor Max Irons.