Officers were called at approximately 8.15pm on Monday, 14 December to reports of a car in collision with a pedestrian on Morden Hall Road.
The London Ambulance Service also attended the scene and the pedestrian, a 66-year-old woman, was taken to hospital for treatment. She remained there in a critical condition, but despite efforts to save her, she died from her injuries on Wednesday, 16 December.
The driver of the car stopped at the scene and is assisting police with enquiries – there has been no arrest.
Officers are keen to speak with anyone who was on board a Route 118 bus that was stationary at a bus stop by Morden Lodge at the time of the collision and may have witnessed the collision.
They would also like to hear from any road users who may have captured in incident on dash-cam footage.
Officers from the Serious Collision Investigation Unit based at Merton are investigating.
Anyone who can assist police is asked to contact the witness appeal line on 020 8543 5157, call 101 or tweet @MetCC and quote CAD 6838/14Dec.