Tinodiwanashe Makwanya was shot in the head as he sat in the passenger side of a Volkswagon car just after 22:00 BST on Friday.
Officers said it is thought a motorcyclist with a pillion passenger pulled up alongside the car on Wellesley Road in Croydon.
The car driver took the victim to hospital, where police were alerted.
Six minutes after police were first called, officers were told Mr Makwanya had died when he arrived at the hospital.
He was shot near Croydon town centre
Det Insp Domenica Catino said: “Croydon town centre would have been busy with people out and about on a Friday night and I would appeal to anyone who was in the area and saw the events unfolding to contact police.
“At this stage we retain an open mind to the motive for this shooting and our enquiries continue.”
No-one has been arrested in connection with the shooting. -BBC