I have the Irish words for the first three verses from a printout I received in Irish language class. Credited as author is Micheál Ó Siochfhradha, brother of Pádraig (An Seabhac).
I see it's from a book of song lyrics because it sits on page 27 facing Rosc Catha na Mumhan by Piaras Mac Gearailt on page 26.
If anyone is familiar with this book as I have only the single page printout, please let me know so I can look into purchasing the whole.

go raibh míle maith agaibh