Avon and Somerset Police said in a full statement: "The M4 is closed in both directions after a body was found on the carriageway between junctions 20 (Almondsbury Interchange) and 21 (Awkley).
Avon and Somerset Police said that the force was called at 6.40pm and human remains were found when officers arrived at the scene.
Enquiries are underway to identify the deceased and the road is expected to remain closed into the early hours of Sunday morning.
The tragic discovery of human remains between junctions 20 and 21 has seen the busy motorway fully closed tonight.
"The road is expected to remain closed into the early hours of Sunday 23 February.
