The acts jointly headline the show at LSO St Luke's in London on Wednesday, October 10.
Proceeds from the event will be donated to War Child to support its work helping children affected by conflict across the world.
The date follows the previously-announced show at the same venue on September 26, which features Jessie Ware, Lianne La Havas and Field Music.
Tickets are available via competitions and a ballot system run by Barclaycard Unwind and The Ticket Factory.
Fans can enter the ballot for 48 hours from 10am today (September 24). Tickets are free but each pair of tickets secured requires a £10 donation to War Child.
Mercury Prize 2012 nominees in pictures - photo gallery:
Copyright: Rex Features Sadaka Edmond/SIPA
All acts confirmed for the Barclaycard Mercury Prize Albums of the Year Live gigs have been nominated for the 2012 award.More gigs featuring nominated artists will be announced in the weeks to come.
Further gigs featuring more of the 2012 shortlisted artists will be announced over the coming weeks.
