The Pala trio will play Camden's Roundhouse in London on July 14, with fans able to apply for free tickets online and through the festival's iPhone/iPod app.
Previously-confirmed acts for the month-long event include Adele, Jessie J, Foo Fighters, Beady Eye, Manic Street Preachers and The Wanted.
Friendly Fires recently told Digital Spy that they feel pressured when performing to a festival crowd because they have to get people enjoying their set quickly.
> Friendly Fires: 'Pala will upset *NSYNC fans' - Video
Watch our exclusive interview with Friendly Fires' Jack Savidge and Edd Gibson below:
Listen to 'Hawaiian Air' by Friendly Fires below: