Emergency crews were called to reports that two men had been stabbed in Hainault at around 10.20pm on Friday.
A 23-year-old man was pronounced dead at the scene, Scotland Yard said.
Another man, aged 22, was taken to an east London hospital where he is in a critical condition.
A police spokesman said: “Work continues to inform all next of kin. A post mortem examination will be scheduled in due course.”
No arrests have been made as yet and a crime scene remains in place, the spokesman added.
Officers from the Metropolitan Police’s homicide and major crime command are investigating.