Police were called at approximately 9.37pm on Monday, 5 April to reports of a collision involving a car and a pedestrian in Romford Road, E15.
Officers attended along with the London Ambulance Service and the pedestrian a 30-year-old man was taken to hospital with life-threatening injuries. His next of kin has been informed.
A 26-year-old was arrested on suspicion of driving while under the influence of drugs. He remains in custody at an east London police station.