The single vehicle incident happened at Ballymacken on the M7 near Portlaoise shortly before ten o'clock last night.
The 47 year old man was pronounced dead at the scene and his body was taken to the Midlands Regional Hospital for a post mortem.
He had been alone in the car and no-one else was injured in the incident.
Gardai closed the road for a time to allow for a forensic examination but it has since re-opened.
