The couple were travelling south on the A629 Western Bypass at 1.20pm on Saturday when their dark red Vauxhall Grandland left the carriageway, North Yorkshire Police said.
It collided with the barrier and fell off the bridge, landing near to the canal on Broughton Road.
The driver of the vehicle, a man from West Yorkshire, was pronounced dead at the scene.
While the female passenger was taken to hospital in a critical condition.
Despite the best effort of medical professionals, she was pronounced dead a short time later.
Their next of kin have been informed, the force added.
Anyone with any information or relevant dashcam footage has been asked to contact TC 123 Geri Tunney at North Yorkshire Police, either via 101 or email email@example.com, quoting reference number 12230200190.