The pedestrian was on the carriageway “for reasons yet to be established” at the time of the collision.
He suffered fatal injuries as a result of the incident between 1.45am and 2am on Saturday morning.
The motorway was closed in both directions between junctions 3 and 4 at Frankley Services near Birmingham while emergency services dealt with the scene.
West Mercia Police said it was not clear why the man was on the carriageway.
”For reasons yet to be established a pedestrian was on the carriageway,” the force said in a statement.
“The pedestrian was struck by a vehicle causing the pedestrian to suffer fatal injuries.”
Police are appealing for any motorists travelling on the M5 near the services to get in contact.
Inspector Russ Barker said: “The M5 is a central route for people travelling across the country and we’re keen to speak to anyone who was on the stretch of the motorway between junction 3 and 4 near to Frankley Services early this morning.”
Motorists had been warned to expect delays as the M5 remained closed in both directions for several hours.
The motorway was fully reopened at around 8.30am with Highways England reporting that "traffic is flowing well in the area."
Any witnesses should contact West Mercia Police on 101.
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