Police were called by the London Ambulance Service at approximately 12:55pm on Wednesday, 13 January following reports of an assault at an address on The Broadway, Merton, SW19.
Officers attended and found a 41-year-old man who had been stabbed.
Despite the efforts of the emergency services, the man was pronounced dead at the scene at 01:55hrs. His next of kin have been informed.
A post-mortem examination will be held in due course.
Two men – aged 33 and 53 – were arrested on suspicion of murder. They were taken to south London police stations where they remain in custody.
Two men, aged in their 20s, who were also arrested and taken into custody have been released with no further action.
Detectives from the Met’s Specialist Crime Command (Homicide) are investigating.
Anyone who can assist officers with their investigation is asked to call police on 101 quoting CAD232/13JAN.
Alternatively, information can be provided to Crimestoppers, anonymously, on 0800 555 111.