Two cars, one carrying two people and the other carrying three, collided around 3:40 a.m.
The man, who was a passenger in the back seat, was pronounced dead on the scene. The other four people — three men and one woman, all in their 20s and 30s — were taken to hospital with serious injuries.
All eastbound lanes of the tunnel were closed for hours while the Quebec provincial police investigated the accident.
The tunnel reopened just before 2 p.m. Saturday.
The circumstances of the crash are still unknown, but Sgt. Claude Denis said one of the cars was split in half.
He said it was too early to say whether speed was a factor.
The four survivors of the collision have severe, but not life-threatening, injuries.