It was adopted due to the blood curdling battle-cry of Sergeant Patrick Masterson as he tore into the French ranks, with Ensign Keogh, to capture the first French Imperial Eagle to be taken in battle - during the Battle of Barossa.
He was then heard to cry 'Be Jabers Boys! I have the Cuckoo!' as he held it triumphantly aloft to rouse the spirits of his men. Alas, Ensign Keogh did not survive the daring dash into the French ranks.
It was popularized outside of Ireland by the Irish Brigade – composed of the 69th New York Volunteer Infantry (NYVI) or "Fighting 69th", the 63rd & 88th NYVI, and later the 116th Pennsylvania and 28th Massachusetts Volunteer Infantries – which fought in the American Civil War.
The motto was also adopted by the 55th Battalion of the Australian 5th Division during the First World War.
Since then it has appeared rather infrequently in spoken language but has enjoyed some popularity in print, appearing on mugs, t-shirts, etc.
Historian and musician Derek Warfield released a book and companion CD, which he entitled "Clear the Way", dealing with the history of the 69th Regiment.
There is also a dam and a road in Bendigo , Australia which is named Faugh A Ballagh.
The phrase is referenced in the Dropkick Murphys ' "The Legend of Finn MacCumhail" and "Heroes From Our Past"