The incident happened in Commercial Road near the Rotherhithe Tunnel just before 9.50pm yesterday (April 3).
Officers and London Ambulance Service crews attended and found a man injured.
He was taken to hospital for treatment where his condition was assessed as life threatening.
The driver, a 19-year-old man, was arrested at the scene on suspicion of causing serious injury by dangerous driving.
He remains in police custody.
A spokesperson for Metropolitan Police said: “Police were called to a collision involving a car and a pedestrian on Commercial Road, Limehouse at 9.47pm on Thursday, 3 April.
“The pedestrian, a man in his 30s, was taken to hospital where he remains in a life-threatening condition.
“The driver, a 19-year-old man, was arrested at the scene on suspicion of causing serious injury by dangerous driving. He remains in custody.
“Commercial Road was closed in both directions for recovery and investigation. It was reopened at around 8am on April 4.
“Witnesses or anyone with any information or footage is asked to call 101 or post on X @MetCC quoting CAD 7951/03Apr.”
