Five cars were hit and police closed both lanes of the M2 to deal with the accident and allow the Air Ambulance to land.
The fatal crash happened near the Duncrue off-slip.
All the emergency services the crash scene with roads in the area closed for six hours, causing widespread disruption.
Inspector Andrew Wilson from the Collision Investigation Unit said: “At approximately 3.50 pm yesterday, Sunday, 22 July, police received several reports of a silver car travelling in the wrong direction along the M3, Belfast from Sydenham bye-pass towards the M2.
“We are working to establish where this vehicle joined the M3 and its subsequent movements prior to the collision.
“I would appeal to anyone who has dash cam footage of this vehicle or information relating to this incident to contact the Collision Investigation Unit at Sprucefield on the non-emergency number 101, quoting reference 1004 22/07/18.
“I also wish to express my thanks to the members of the public who have already come forward and provided us with dash cam footage and witness accounts leading up to this road traffic collision.”