In Gaul, Maewyn changed his name to Patrick (a more Christian name) and studied in a monastery for twelve years. He came to believe that it was his calling to tell the people of Ireland about God, so he returned to there. When he was telling people about God, he used the shamrock, which resembles a three-leafed clover, to help explain the concept of the Trinity (father, son, holy spirit).

Patrick was arrested several times, but escaped each time. He traveled throughout Ireland, establishing monasteries and setting up schools and churches to aid in converting the Irish country to Christianity.

Patrick's mission in Ireland lasted for thirty years. He then retired to County Down and died on March 17 in 461 AD. That day has been commemorated as St. Patrick's Day ever since.