The incident happened on the A259 at Peacehaven just after 11.10pm yesterday.
The man, who was 27, was seriously injured after being hit near the junction of Dorothy Avenue.
He was pronounced dead at the scene.
As the incident involved a police vehicle, the matter has been referred to the Independent Office for Police Conduct (IOPC) who will carry out an independent investigation.
A section of the A259 South Coast Road was closed in both directions for the investigation but has now re-opened.
A closure with the junction of Bramber Avenue remains in place however.
Chief Superintendent Jo Banks said: ‘This is a tragic incident and we are fully supporting the IOPC investigation. We want to thank drivers and residents for their patience while the A259 South Coast Road was closed.’
In the meantime, police are urging anyone with information or dash cam footage of the incident to email [email protected] quoting Operation Ambleside.