The man, who was in his late 20s, was riding a motorbike which collided with a car on the old Portlaoise to Ballybrittas road at The Heath at around 7:20pm.
He died a short time later in Portlaoise hospital.
The driver of the car, a 75-year-old woman, was also taken to hospital with non-life threatening injuries.
The road is expected to remain closed until later today to facilitate a forensic examination and diversions are in place.
Gardaí are appealing for witnesses.
