Patrick spent twenty years of his life as a monk in Marmoutier Abbey. There he again received a celestial visitation, this time calling him to return to the land where he has been enslaved, though now with a mission as a priest and converter. Patrick was called to Rome in 432 whereupon Pope Celestine bequeathed the honour of Bishop upon him before he left on his holy mission.
Patrick and 24 of his followers arrived in Ireland in the winter of 432. In the Spring, Patrick decided to confront the high King of Tara, the most powerful King in Ireland. Patrick knew that if he had the King's support he would be free to take God's message to the people of Ireland.
Patrick and his followers were invited to Tara by the King of Laoghaire. While he was there he plucked a shamrock from the ground and tried to explain the to the druids and the King that the shamrock had three leaves just like God had three personas – The Father, The Son and the Holy Ghost. This was called the Trinity.
King Laoghaire was very impressed and chose to accept Christianity. He also gave Patrick the freedom to spread Christianity throughout Ireland.
St. Patrick is also known to have driven the snakes out of Ireland. However, the snakes were at that time a symbol of Paganism, and it was the Pagans that were driven out.
Patrick is thought to have died sometime between 463 AD and 493 AD. There is a dispute as to his place of burial; the site with the strongest claim seems to be Down Cathedral, where a large slab of rock on which the word Patric is inscribed protects 'the grave' of St Patrick.