Officers were called around 3.15am on Friday (May 28) to reports of a single vehicle collision involving a grey Toyota Proace van on the A23 London Road, at the junction with Manor Royal.
A 25-year-old man from East Grinstead suffered serious injuries and sadly was pronounced dead at the scene.
Officers are appealing to anyone who witnessed what happened, or who has relevant dash-cam footage that may assist with enquiries, to come forwards.
London Road remains partially closed in both directions while vehicle recovery work is ongoing.
Anyone with information, or who saw the vehicle prior to the collision, is urged to report online or call 101, quoting Operation Lynton.