The incident happened in the early hours of Friday morning and led to the closure of the A14 in both directions between Wherstead (junction 56) and Nacton (junction 57).
Officers were called by the ambulance service at 3.14am to reports of a person in the westbound carriageway on the Orwell Bridge.
Further reports were received from members of the public.
Emergency services attended and a male was pronounced deceased at the scene.
The individual has not been identified.
The closure has caused significant delays in and around Ipswich throughout the day.
A spokesman for Suffolk Police said: “Officers are appealing for any witnesses and asking any motorists driving in the area at the time of the incident with a dashcam fitted in their vehicle, to review the footage for any material that may be of assistance.”
The A14 remains closed.
Diversion routes have been put in place to help manage traffic.
Westbound drivers are advised to exit the A14 at junction 58 and follow the A1156 Felixstowe Road, then take the A1214 around Ipswich to rejoin the A14 at junction 55, Copdock Roundabout.
Eastbound drivers should exit at junction 55 and follow the A1214 to the Woodbridge Road Roundabout, then take the A1189 to rejoin the A14 at junction 58.
Enquiries remain ongoing.