Police were called at around 11.45pm on Thursday to Boundary Road in South Hampstead. They found a 20-year-old man and a 22-year-old man suffering stab injuries.
Both were taken to hospital, where the 20-year-old man was pronounced dead, police said. Officers believed they knew his identity and were informing his next of kin. The 22-year-old man is not thought to have been critically injured.
No arrests had yet been made, police said.