They are joined on the bill for the festivals by Sub Focus and Boy Better Know.
[Left: Alt-J / Right: Deftones]
"More music, more stages, more epic times," the festival sites promise. "Lots more bands coming soon."
It was recently confirmed that the festivals would feature three new stages in 2013, while capacity would remain the same size.
Festival Republic boss Melvin Benn said: "I've got quite a strong buzz and feeling in myself in the changes that I'm making there.
"I'm still formulating the ideas. There will be quite a bit more dance music, quite a bit more other bits and pieces."
Reading Festival takes place August 23-25 at Richfield Avenue. Leeds Festival takes place over the same weekend at Bramham Park.
Reading and Leeds Festivals 2012: photo gallery