The committed Catholic's rendition of the hymn, Make Me a Channel of Your Peace, was heard across the a park in Glasgow as Pope Benedict XVI was saying his farewells to church leaders following mass.
Around 65,000 people had attended the ceremony in Bellahouston Park where, about three hours earlier, Boyle, 49, was met with waving white and pale yellow Papal flags and enthusiastic applause as she helped herald his visit.
Dressed in an elegant long black coat and black heels, her flawless rendition of her signature I Dreamed a Dream and hymn How Great Thou Art brought the crowd to their feet and inspired many to sing along with her.
Monica Alford from Greenock, Scotland said, "She was marvelous, made the hairs stand up on the back of my neck. She just moved me."
Susan Lafferty, 48, brought her daughter Jennifer, 10, from the Uddingston neighborhood of Glasgow. "She was brilliant," says Lafferty, who teaches secondary school, "She's just such a fantastic story. I think she's great."
"It's something I've always dreamed of, it's something I've always wanted to do, and here I am, finally getting the chance," Boyle told Sky News.