Police were called at 09:04hrs on Monday, 7 January, to Balham Hill, SW12 to a report of van in collision with a pedestrian.
London Ambulance Service attended the scene and took the victim to a south London hospital.
The victim is a 37-year-old man who suffered a serious head injury. His injury is considered life-threatening.
The man’s next of kin have been informed.
The driver of the Mercedes van stopped at the scene and is co-operating with police. No arrests have been made.
Any witnesses or anyone with any information is asked to call the Serious Collision Investigation Unit on 020 8543 5157 quoting CAD/158107JAN19.
To give information anonymously contact Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org.