At around 11.30am the man is believed to have ran up the exit slip road on the M1 southbound at junction 11 and onto the motorway.
He then ran across the lanes before he was struck by a black Range Rover in lane four of the motorway.
Emergency services attended but sadly the man was pronounced dead at the scene. His next of kin have been informed.
Sgt Doug Fishwick, of the Beds, Cambs, and Herts roads policing unit, said: “This was a tragic incident and our thoughts are with the family of the man who died.
“I’m appealing for anyone who witnessed the incident, or who saw the man in the area of the M1 prior to the collision, to get in touch so that we can establish what happened. The man was not believed to be wearing a top or shoes.”
Anyone with information is asked to contact police on 101 quoting reference 140 of 21 June.