As for the author, I checked all my songbooks last night. About ten with this song in them don't mention it or state 'anonymous'. Three mention an author. Soodlum's as posted above by Big Tim.
C. O'Boyle, Songs of Co. Down, says 'Canon Charles O'Neill'
C.D. Greaves, The Easter rising in song and ballads, says 'Rev. P. O'Neill'

Nothing conclusive. I'm surprised that less than a century after the song was written, the authorship can be under debate.

Wolfgang