The American heavy-metal band will headline the Pyramid Stage June 28.
"Isn't that incredible? I'm so pleased to have them," festival organizer Michael Eavis said in an interview posted on the event's website.
"Metallica are one of the most popular bands in the world! And they really are a phenomenal live act. This is a band that can sell out stadiums in pretty much every country on the planet. From Newlyn to Newcastle on my travels, all through the years, people keep asking me, 'When are Metallica going to play?' There's a huge swathe of people who love Metallica to bits and just think they're absolutely amazing. They're worthy headliners!"
The musicians will join previously announced headliners Arcade Fire, who will play June 27, and Kasabian, who will close the festival June 29.
The War On Drugs, Nick Mulvey and English National Ballet have also been added to the lineup for the festival, which will kick off June 25 at Worthy Farm in Pilton.