Police were called at 8.29pm on Tuesday, 3 December to reports of gunshots heard on Walterton Road, W9.
Officers attended and found a man, believed to be aged in his late teens, suffering from a gunshot injury.
The London Ambulance Service also attended. The man has been taken to hospital where he is in a critical condition.
At this early stage, there have been no arrests.
Anyone with information is asked to call police via 101 quoting reference Cad 7338/3Dec.