The incident happened around 11am on Monday on the A736, Glasgow Road, just south of its junction with Hurlet Road.
A 60-year-old woman, the pedestrian, was taken to the Queen Elizabeth University Hospital with serious injuries.
A 33-year-old man, the driver of one of the cars, also sustained serious injuries and was taken to the Queen Elizabeth University Hospital.
The second driver, a 54-year old man, was taken to the Royal Alexandra Hospital, Paisley, with serious injuries.
Sergeant David Bulloch said: “This was a serious crash and we’re working to establish the full circumstances.
“I would ask anyone who may have dash-cam footage of a white Vauxhall that can help with our investigation to get in touch. I would also ask anyone with private CCTV to contact us.”
Anyone with information should call 101, quoting incident number 1176 of Monday, 14 June, 2021.