Paramedics from Dublin Fire Rescue and Emergency Ambulance Service helped to deliver the child who was born on the M50, near Ballymun, overnight.
An ambulance and a fire engine were sent to junction 4 of the M50 at 03:30 local time on Sunday. The baby was born in the front seat of the car at 03:45.
Both mother and child were taken to the Coombe Women and Infants Hospital and are said to be "doing well".
The child's name has not been released.
A woman has given birth to a baby girl on a motorway in County Dublin.