The teen victim was found discovered with stab injuries inside Lordship Recreation Ground in Tottenham, Haringey, at around 2.15pm on August 1.
He was taken to hospital where he died today, the Met Police said.
Police said a 16-year-old boy arrested on suspicion of attempted murder on August 5 was taken to hospital for treatment unrelated to the incident and later returned to custody. He has since been released on bail.
A second 16-year-old boy who was arrested on suspicion of attempted murder on August 7 has also been released on bail.
Detective chief inspector Neil Rawlinson, from the Met’s Specialist Crime and who is leading the investigation, said: “We are making progress with our enquiries but we know there are people who witnessed this attack or who have details about what happened and have not yet spoken to us.
“This stabbing happened in the middle of the afternoon when the area would have been busy.