A man in his 50s has been arrested in connection with the collision - he's being held at Kildare Garda Station under Section 4 of the Criminal Justice Act.
It happened at around 8pm on Thomas Street in Newbridge last night where a woman in her 40s was found with serious injuries.
She was taken to Naas General Hospital where she was pronounced a short time later.
Gardaí say the results of a post-mortem will determine the course of the investigation.
Anyone with information to the incident or has dashcam footage are being asked to contact Newbridge Garda Station.