The man was crossing Abbot Adams Bridge in Main Street, Kilwinning, at about 03:00 when he was hit by a blue Vauxhall Corsa.
He was taken to Crosshouse Hospital, Kilmarnock, where his condition was described as serious but stable.
Police say the car drove off towards Irvine and have appealed for witnesses.
Sgt Ian Thornton said: "Inquiries are ongoing into the circumstances surrounding this collision.
"Officers have been checking all available CCTV systems and have been speaking to witnesses who came to the man's aid.
"I would appeal to the driver of the Corsa to come forward and contact police as a matter of urgency.
"Similarly, I would ask anyone who witnessed the collision, or the Vauxhall Corsa being driven, to contact the Divisional Road Policing Unit at Irvine via the police non-emergency number 101 or Crimestoppers on 0800 555 111."
A 51-year-old man has suffered serious injuries after being struck by a car in a hit-and-run incident in North Ayrshire.