Oxfordshire Fire and Rescue service received a call at 10.21am to a serious road traffic collision on the southbound carriageway between junctions 12 (Gaydon) and 11 (Banbury) of the M40 motorway.
The incident involved one vehicle, carrying three people, which left the road.
One person was confirmed dead at the scene.
Two fire appliances from Warwickshire Fire and Rescue service also attended the scene.
Due to the seriousness of the incident, it is being investigated by Thames Valley Police.