Where does the phrase "luck of the Irish" come from?

Answer 1

This is one explanation I unearthed. St. Patrick is said to be at the origin of this saying. He was a kidnapped Briton who was enslaved and found God on the hills herding sheep as a slave. He escaped and to cut a long story short became a Bishop and returned to Ireland to bring the faith to the pagan Irish who believed in the druidic religion.
He received inspiration from God to use the trefoil called the shamrock to explain the Trinity to his flocks, the Celts and the descendants of the Viking invaders, who believed in the druidic religion of magic and pantheistic gods. The existence of four leaf clover was explained by the fact that God melted the druid beliefs with the Trinity of the Christian faith.
Irish soldiers conscripted into the British army began wearing the shamrock on their uniforms to bring them "magic" and avoid being killed in battle. (Because they were blessed and used by St. Patrick they believed they were on God's side and protected by God.)
This is known as "wearing the gteen".
The Irish are descendants of great fighters and invaders: the Celts and Vikings. They truly seem to be lucky because they are good at what they do and fewer get killed because of their natural fighting skills. "The Luck of the Irish"

Answer 2

I really wonder that myself, having a bit of Irish in my blood, I sure am not a lucky person. Unless that is the luck of the Irish.