Byrne-Costigan was appointed professor of Romance languages at
University College Cork (UCC) in 1939, after the retirement of
Mary Ryan. She stayed in this position until 1969, establishing the Italian department and introducing a refresher course for French teachers. Her academic publications focused on studies of
Le bourgeois gentilhomme by
Molière,
Athalie by
Jean Racine, and
Horace by
Pierre Corneille. She translated
Le mie prigioni by
Silvio Pellico into Irish, which is held by the Pellico Museum in
Turin. Her Irish translation of a collection of
Salvatore Quasimodo's poems was published by the Italian Institute. She founded the
Dante Alighieri Society in Cork with Dr Piero Calì, serving as the president from 1956 to 1969. She retired from UCC, taking up part-time lecturing at
Trinity College Dublin on Italian philology and medieval texts. Byrne-Costigan was a member of the Irish national committee of
UNESCO, and represented Ireland twice at the biennial UNESCO conference in Paris. She was also the honorary secretary of the
Celtic Congress. In 1960 she was made a Grand Officer
Order of Merit of the Italian Republic for her work on promoting Italian culture and the language in Ireland. ==Later life and legacy==