The British band after scheduled to appear at the castle in Aberdeen, Scotland, later this month, when the 'Game of Thrones' stars will tie the knot in front of 200 of their closest friends and family.
A source told The Sun newspaper: ''Kit and Rosie are huge fans, so they jumped at the opportunity to get Mumford & Sons to perform at their wedding.
''Kit met the boys on Graham Norton's show in 2015 and he's kept in touch with them ever since.
''He was thrilled when the band agreed. They can't wait either. It's a once-in-a-lifetime gig given the very 'Game Of Thrones' setting.''
Kit, 31, and Rose - who played lovers Jon Snow and Ygritte in the HBO fantasy series - confirmed their engagement by posting an announcement in the Forthcoming Marriages section of The Times newspaper.
It read: ''The engagement is announced between Kit, younger son of David and Deborah Harington of Worcestershire, and Rose, middle daughter of Sebastian and Candy Leslie of Aberdeenshire.''
In 2017, the high-profile couple splashed out £1.75 million on a seven-bedroom countryside home in East Anglia, England, and Kit has since confessed he loves living with Rose.
He said: ''Me and Rose, my girlfriend, said we need a few months together in London for some downtime. We've just moved in together. I've never lived with a partner before. It's amazing.''
Meanwhile, Kit previously revealed it was ''very easy'' to fall in love with the 31-year-old actress because their characters were so close in 'Game of Thrones'
The London-born star said: ''If you're already attracted to someone, and then they play your love interest in the show, it becomes very easy to fall in love.''
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