It's understood the motorist was travelling on the B742 early this morning when the tragedy happened.
She died at the scene.
The road was closed to allow an investigation to take place. No other vehicles were involved.
A spokesperson for Police Scotland said: "Police were called to a report of a one-vehicle road crash on the B742 in Darlymple near to the viaduct at around 7.30am this morning.
"Emergency services attended and the female driver of the vehicle was pronounced dead at the scene."
"The woman is still to be formally identified and enquires are at an early stage."
Following today's tragedy Police Scotland officers at Ayrshire Division's Road Policing team are appealing for witnesses and information.
A spokesperson said: "Emergency services were called to a report of a blue Ford Fiesta found off the B742 near to Burnton Viaduct.
"The driver of the vehicle, a 74 year old woman, was found within the vehicle. She was pronounced dead at the scene.
"The death is currently being treated as unexplained at this time.
"A post mortem will be carried out in due course to establish the exact cause of death."
Anyone with any information is asked to contact police via 101 quoting reference number 0586.
