A woman fell from a bridge over the motorway at junction three, near Nursling, and died at the scene. No-one else was injured.
Thousands of motorists were caught up in the resulting chaos as the westbound carriageway was closed during the evening rush hour.
The motorway fully reopened at 01:00 on Friday.
Nine people had to be treated in hospital for shock after witnessing an incident on the M27 at Southampton.