An Isuzu truck and car collided on the Hume Freeway, near the Samaria Road overpass, about 12.30am.
The driver of the car, a man aged in his 70s, was airlifted to Melbourne with life-threatening head injuries.
The driver of the truck, a 22-year-old Mill Park Man, was treated at the scene for minor injuries.
He was arrested about 11.30am and is currently assisting investigators with their enquiries.
Detectives are appealing for any witnesses who stopped at the crash scene to speak to police.
Investigators would also like to speak to anyone with dashcam footage that was travelling along the Hume Freeway in the Benalla area prior to the collision.
Any witnesses or anyone with dashcam footage is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au