Boyle, the unlikely pop star who shot to global Internet fame after she sang on the TV show "Britain's Got Talent," was to reprise her winning performance of "I Dreamed a Dream" from "Les Miserables" during a Mass on Thursday celebrated by Pope Benedict XVI.
Boyle was also joining an 800-strong choir in singing hymns at Glasgow's Bellahouston Park.
In a pre-Mass statement, the Scottish-born Boyle said "it's a great honor to sing for the pope and it's something I've always dreamed of."
Benedict was capping off his first day of a four-day state visit to Britain that included a meeting with Queen Elizabeth II at Holyroodhouse Palace in Edinburgh.