The incident is understood to have happened in the Cabra area last Sunday.
The Herald reports the 10 month old child was left at the side of the road, after the car-thief didn't realise the infant was in the back seat.
The man watched as a couple left the car engine running, and briefly went inside their home.
At the time, their two children were in the car and their 9 year-old, managed to jump from the car before the man sped off.
However the car-jacker didn't realise there was an infant strapped into the back seat.
Shortly afterwards the child was left in its car seat on a footpath and the car-jacker continued driving.
No one has been arrested and no description of the man has been issued.
