Emergency Services were called at 6.39am today to reports of a collision involving three vehicles between junctions 8 and 9 on the southbound carriageway.
Initial investigations indicate that there was a collision involving a Mitsubishi ASX 4 and a Skoda Superb, which resulted in the driver of the Mitsubishi getting out of his vehicle.
The 37-year-old man, from Southampton, was then struck by a third vehicle, a Citroen Berlingo.
Sadly, he was pronounced dead at the scene.
The drivers of the two other vehicles were uninjured.
As a result of the collision, the stretch of motorway was closed to allow for officers to conduct their investigations into the exact circumstances of the incident.
The road was reopened just before midday.
Roads Policing Sergeant Barry Long, from the Joint Operations Unit, said: “We know that closing such major route for several hours causes huge inconvenience for motorists but we would like to thank all those caught up in the back log for their patience and understanding that we will always do our best to reopen roads as quickly as possible.
“We have already spoken to many motorists who witnessed what happened this morning but if there are any other witnesses who have yet to speak us, please get in touch.
“We would also like to speak to anyone who saw any of the vehicles prior to the collision.”
Anyone with information is asked to contact Sgt Long on 101, quoting 44160391970, or Crimestoppers anonymously on 0800 555 11