The 'Empire State Of Mind' star has been added to the line-up for the station's biggest ever free concert, which is to take place over the weekend of June 23 and 24.
Flo Rida, Sean Paul, Azealia Banks and Tinchy Stryder were previously added to the bill in an announcement last month.
Florence + the Machine, Leona Lewis, will.i.am, Jessie J, Ed Sheeran and Lana Del Rey are also among those playing at the two-day event.
Another act, described by the BBC as an "international superstar", will be announced in the coming weeks to headline Sunday, June 24's bill.
BBC Radio 1's Hackney Weekend 2012 will be staged across two days, and see over 100 UK and international artists performing on six BBC stages.
Tickets are free, but there will be a small fee of £2.50 per ticket to cover ticket handling and administration costs.
Radio 1 listeners must register their interest to attend and upload a photo at bbc.co.uk/radio1 before the closing date of 11pm on March 19.
Watch Jay-Z in the video for 'Empire State Of Mind' below: