The 29-year-old man was found injured and given first aid by paramedics at the scene.
Officers were called by the London Ambulance Service to the scene at the Abbey estate near St John’s Wood just after 7.30pm on Friday.
A man was taken to hospital but died later that evening.
A cordon is in place at the scene near London’s famous Abbey Road while detectives, who have launched a murder investigation, continue their inquiries.
No arrests have been made “at this early stage”, Scotland Yard said.
The family of the victim have been informed and a post-mortem examination will take place in due course.
Detective Chief Inspector Neil Rawlinson, who is leading the investigation, said: “We would like to speak to anyone who was in the area of Abbey estate on Friday night between 7pm and 8pm, who may have seen or heard something they believe could be connected to this fatal stabbing.
“Another family have been left grieving the loss of a loved one due to knife crime.
“My team of detectives are working around the clock to identify and arrest the person responsible.”
There were 104 murders in the capital between January 1 and December 7 this year, the force said.