She was born as Ilona Zimka near Budapest. She married Istvan Hertelendy in 1940. She became a successful stage actress with the Hungarian Repertory Theatre “VIGSZINHAZ” in Budapest, playing such roles as Ophelia (Hamlet), Irina (Chekhov's Three Sisters), in Molnar's Liliom and in J.B. Priestley's An Inspector Calls.
She continued to act on television in such series as Peter Gunn, Perry Mason, Barnaby Jones, Ironside, Marcus Welby, M.D., The Fugitive, Dr. Kildare, and Columbo. Among her television roles was as murderer Helga Dolwig in the 1965 Perry Mason episode, "The Case of the Impetuous Imp." Notable films in which she appeared include Five Minutes to Live (1961), Harlow (1965), Convict Stage (1965), In Like Flint (1967), Rosemary's Baby (1968), The Girl from Petrovka (1974), Two-Minute Warning (1976), Raid on Entebbe (1977), Being There (1979), Christmas Lilies of the Field (1979) and Circle of Power (1981). Others included independent films such as Return (1985).
Hanna Hertelendy was the third and last wife of film star Robert Walker, whom she married on July 27, 1949. Walker died at the age of 32 in 1951, reportedly due to an allergic reaction to a drug administered by his psychiatrist. Hertelendy was married four times; her last husband was Hungarian-American actor Stephen Bekassy. She had one child, from her marriage to William Kerwin, with whom she was married from 1953 until their 1958 divorce.
She died in her West Hollywood, California home on May 15, 2008, aged 88.