Denis Glennon made the promise to his daughter Ciara at her graveside in March 1997, after she was abducted and murdered in Perth.
Originally from Westport, Mr Glennon worked for Bord na Móna before moving to Australia with his family, where Ciara was raised according to the Western People.
“Through tears, I said she would fight for her life because of the way she was brought up… she would fight for her life," he said.
“Little did we know then how prophetic those words would be. As she fought to save her life, she left us the vital DNA clues.”
Traces of DNA were found under Ciara's finger nails, which were able to be re-examined years later due to advancements in forensic science.
The DNA helped to identify Bradley Edwards (51), who was convicted in the West Australian Supreme Court in Perth yesterday for the murders of Ms Glennon and another woman, Jane Rimmer (23) in 1997 and 1996 respectively.
Mr Edwards was acquitted of the murder of a third woman whose body has not been found.
Speaking after the judgement, Mr Glennon recalled the promise he made to Ciara 23 years ago.
“After her funeral, I visited her grave alone and made a personal commitment to her. I told her I would do all in my power to find the person or persons responsible for killing her or I would die trying.
“Since then, that promise to Ciara has driven me unwaveringly and unapologetically.”
Referring to a statement he had made in 2012, Mr Glennon said: “There’s always somebody missing, a conspicuous absence, an empty chair. Her silence speaks louder than our words. We miss her acutely.”
Mr Glennon said those words from eight years ago still “resonate today with imperishable clarity and meaning”.
