Kent Police have said the pedestrian was pronounced dead at the scene. The clockwise carriageway of the M25 between junctions 3 and 4 is likely to remain closed until around 11am.
Any witnesses or anyone with information are asked to contact Kent Police on 01622 798538.
More top news
Goals from Charlie Austin, Dusan Tadic and James Ward-Prowse consigned Slaven Bilic's men to their fourth straight Premier League loss.
A bizarre protest against BP sponsorship at the British Museum used theatre, sea shanties and 'mermaids' to 'summon a Kraken'.
Two men have been jailed for robbing a man aged 79 as he was washing his car.