It's not the first time the band have taken to the main stage, having made their debut at the event back in 2003.
"I can't stop thinking about playing at Reading & Leeds," said The Libertines frontman Pete Doherty.
"There is a great vibe in the band and we should be doing some new songs too. So it'll be the best Reading and Leeds ever," added band-mate Gary Powell.
The festival takes place on 28-30 August.
Mumford and Sons and Metallica have already been confirmed as the two other main stage headliners.
Mumford and Sons last appeared at Reading and Leeds on the NME/BBC Radio 1 Stage five years ago.
The band have been working on their third album since February 2014.
Festival boss Melvin Benn announced another 50 acts that will perform for fans across the English bank holiday weekend.
They include Jamie XX, Gorgon City, Kendrick Lamar and The Maccabees.
"I really think we've got the ultimate line-up this year," Benn said.
"Where else can you see Kendrick Lamar on the same day as Deadmau5 and Years & Years, or Marmozets on the same day as Azealia Banks or Metallica, or All Time Low on the same day as Knife Party or Mumford & Sons."
Rebel Sound are another of the acts confirmed to play.
"The last time we played Reading and Leeds, the crowd were insane and we had to stop the set four times - there was so much energy," the group said.
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The Libertines have been announced as the final headliners for Reading and Leeds Festival 2015.