He was hit by a Volkswagen van on the westbound carriageway near Askham Bryan in the early hours of Sunday morning. Police believe a second vehicle may also have been involved.
The man was seen wearing a top with a distinctive pattern near Askham Bryan College shortly before the incident at 12.50am.
North Yorkshire Police have appealed for anyone who witnessed the collision, saw the man's prior movements or who has dashcam footage to come forward.
Anyone with any information or footage is asked to contact North Yorkshire Police on 101 quoting reference 12210068396, or email PC Nicola Gill at [email protected]
Two people were also seriously injured in a separate collision on the A64 on the afternoon of Friday February 26.
A white Transit van travelling from Strensall towards Stockton-on-the-Forest collided with a red Audi travelling from Malton towards York at the Towthorpe crossroads at 2.20pm.
Police have not revealed which cars the two victims were travelling in.
Anyone who saw the collision, or either vehicle prior to it, is asked to contact North Yorkshire Police by phone on 101 or email [email protected] quoting incident reference 12210067383.