The band will top the bill at the Donington Park-based festival when it takes place between June 8-10, 2012.
The rockers confirmed that they will play their 1991 self-titled album, also known as The Black Album, in its entirety for the festival's tenth year.
Asked why they decided to do the gig, drummer Lars Ulrich told Kerrang!: "The people at Download asked. It wasn't our idea.
"The thing is, although we haven't played at Donington for six years, we have been to the UK pretty much every single summer since then."
He added: "So they wanted us to do something different, and that's what they came up with. I quite like the fact that come next summer it'll be the 21st anniversary of The Black Album, not the 20th."
Ulrich confirmed that there are some songs from the record - 'Don't Tread On Me' and 'The Struggle Within' - that they have never played live before.
Asked whether they would have to relearn them, he responded: "Yeah. Although to be honest with you, a song like 'The Struggle Within' is a lot easier to relearn than 'The Frayed Ends Of Sanity'.
"I don't think it's going to be too difficult for us to figure out these songs."
Metallica recently teamed up with Lou Reed to release a collaborative album named Lulu.
Listen to Metallica's 'The Struggle Within' below: