The rapper was already scheduled to be in the UK throughout the summer as he tours with Kanye West.
The news is a huge added bonus for organisers of the free-ticket show who have already signed several big names to perform at the June festival.
Jay-Z will headline on the main stage joining the likes of Tinie Tempah, Tinchy Stryder, Ed Sheeran, Jessie J, Jack White, will.i.am, Lana Del Rey, The Maccabees as well as Scout London favourite and local boy Michael Kiwanuka.
100,000 free tickets are being made available to the public via a lottery. Those wishing to put their names in the hat will need to register their details (providing a digital passport photo) by 11.00 on March 19.
With London 2012 in mind, 15% of tickets have been set aside for those living in one of the six Olympic boroughs (Hackney, Newham, Greenwich, Waltham Forest, Tower Hamlets, Barking and Dagenham). Tickets for residents of these boroughs will be on a first come first served basis.
For those pinning their hopes on the lottery, tickets will be released in two batches, at 11.00 on 25 March and 16.00 the following day.
Radio 1′s Hackney Weekend