The white BMW they were travelling in left the northbound carriageway at around 9pm between junction 14 (Falfield) and the Michaelwood services.
The M5 remained closed in both directions between junctions 14 and 13 (Stroud) on Saturday morning for collision investigation and vehicle recovery.
Inspector Mark Vicary of Avon and Somerset Police expressed his condolences and stated that the road closures would remain in place for several hours while investigations and repairs were completed.