The victims, a man and a woman, both in their twenties, were pronounced dead at the scene on Runshaw Lane, Euxton last night.
Police say it appears the vehicle, a Fiat Punto, failed to negotiate a sharp bend and careered into the ditch.
The female driver and male front seat passenger were found in the wreckage of the car.
A police spokesman said: “We got a call just after 11pm from a passing motorist reporting a car in a ditch near to the Plough public house.
“Patrols attended and found the vehicle. Sadly the two occupants were pronounced dead at the scene.
“We are appealing for anyone who saw this tragic accident to contact us on 101.”