A 20-year-old man was killed, while a 22-year-old man remains in hospital, following the knife attack in South Hampstead on Thursday night.
The suspects, aged 20 and 23, were arrested after armed officers stopped a blue Audi A3 and are being held in police custody.
Detectives confirmed another stabbing in West Kilburn, west London, is linked to the murder investigation.
In the second incident, a 20-year-old man was taken to hospital suffering from a stab wound to the leg after police were called to Lancefield Street just after midnight.
Officers believe they know the identity of the man who was killed in South Hampstead and are informing his next of kin. A post-mortem examination and formal identification will follow.
Metropolitan Police were called at around 11.45pm on Thursday to Boundary Road in the north London neighbourhood, where two victims were found with stab injuries.
Both were taken to hospital, where the 20-year-old was pronounced dead. The 22-year-old man is not thought to have been critically injured.
Detective Chief Inspector Simon Stancombe, from the Met’s Specialist Crime team, said: “My team is working hard to establish the circumstances of this violent incident, and our thoughts and condolences are with the family of the man who died last night.
“The two arrests were made following an armed stop of a blue, Audi A3 in the early hours of this morning in Shirland Road, NW9.
“This has already been a fast paced investigation and these efforts will continue throughout the coming hours and days."
Anyone with information is asked to call police on 101 quoting CAD 10016/july25, or Crimestoppers, anonymously, on 0800 555 111.
Additional reporting by PA