Police were called to Camden High Street, close to Greenland Road, at about 03:45 BST.
They found a man believed to be in his 30s. He was taken to hospital and later died.
The Metropolitan Police urged bus and taxi drivers and anyone else who may have witnessed the stabbing to come forward.
The victim has not been formally identified yet and a post-mortem examination will take place in due course.
Det Ch Insp Noel McHugh said: "I would appeal to anyone who was in the area of Camden Town Underground Station or the high street at the time of the stabbing to contact police.
"It is possible that you may have information that will help us establish what led to the murder."
Anyone with information has been asked to contact police or to call Crimestoppers anonymously.
A murder investigation has been started after a man was found with fatal stab wounds in north London.