The pair will duet during the Christmas Tree Sessions at Union Chapel, Islington on December 14 and are welcoming song suggestions via the Twitter hashtag #XMASTREESESSIONS.
Spiritualized, Band of Skulls, Fyfe Dangerfield, Josh Kumra, Kodaline and Summer Camp will also perform.
They will be joined by Caitlin Moran, Stuart Maconie, Lee Nelson, Bond, Amy Key, Matt Barbet and VV Brown.
Save the Children will live stream the gig globally on its YouTube channel and the concert will also be available on demand soon after the show and throughout December.
Tickets for the intimate event, which will include mulled wine, mince pies and an audience sing-a-long, cost £40 (plus booking fee) and are available on Ticketline.