The US 'Sex on Fire' rockers and the pop duo will take to the stage along with Sigur Ros, Paramore, Vampire Weekend, Bahamas and Ludovico Einaudi for an all-star line-up at the music festival, held at London's Roundhouse venue.
King of Leon - which is made up of brothers Caleb Followill, Jared Followill, Nathan Followill and their cousin Matthew Followill - enthused: ''We're looking forward to playing this year's iTunes Festival. It's always been something we've wanted to do.''
'Down with the Trumpets' hitmakers Rizzle Kicks - Jordan Stephens and Harley Alexander-Sule - are over the moon after being invited to play at the event, saying: ''One of our most memorable performances last year was playing at The Roundhouse, so we're extremely excited that we're getting the chance to play there again so soon... THANK YOU iTUNES!''
Justin Timberlake and Jessie J will already been announced as headlining at the month-long event, along with other acts including Thirty Seconds to Mars, Jack Johnson, Primal Scream, Jake Bugg, Phoenix and Queens Of The Stone Age.
The shows - run by technology giant Apple - will bring together over 60 acts during each day in September, with many more still to be announced.
Performances can be watched live or on-demand by millions of iOS users around the world as well as via iTunes online or with Apple TV.
UK fans can win tickets using the iTunes Festival app and the iTunes Store as well as select media partners including Channel 4, Global Radio and Metro.
The current line-up for the iTunes festival 2013:
Sept 02 - Sigur Rós
Sept 04 - Paramore
Sept 05 - Rizzle Kicks
Sept 06 - Queens of The Stone Age
Sept 07 - Phoenix
Sept 08 - Kings of Leon
Sept 15 - Vampire Weekend
Sept 16 - Jack Johnson + Bahamas
Sept 17 - Ludovico Einaudi
Sept 18 - Thirty Seconds to Mars
Sept 20 - Primal Scream
Sept 23 - Jessie J
Sept 29 - Justin Timberlake