In the same borough just hours earlier a man in his 50s died outside a bookmakers in Upper Clapton Road following a suspected fight, the Met said.
The two deaths take the total number of people killed in the capital so far this year to 50.
Scotland Yard said officers were approached by a man in his twenties suffering from stab injuries shortly before 8pm on Wednesday on Link Street in Hackney.
The Met said in a statement: "Officers immediately provided the man with first aid.
"The London Ambulance Service and London's Air Ambulance attended.
"The man, who is believed to be aged in his early 20s, was pronounced dead at the scene at 20.24."
The statement continued: "Next of kin are yet to be informed.
"A post-mortem examination will be held in due course. The Homicide and Major Crime Command has been notified.
"A crime scene remains in place. There have been no arrests."
Earlier this week a 16-year-old boy became the youngest murder victim in London so far this year after he was fatally shot.
The teenager, who was shot in the face in Walthamstow, east London, at around 10pm on Monday night, died in hospital with his family by his bedside on Tuesday evening.