The car had been stolen from a Chipotle restaurant in Fontana after the mother left the vehicle unattended with the keys inside for a short time, police said.
The child, who is about seven weeks old, was left inside when the car was taken.
The woman told investigators her child was asleep when she pulled up to the restaurant at 10515 Sierra Ave. She had pre-ordered her food and then parked in a handicapped spot and left the car running with the air-conditioning on while she went inside to pick up her order.
A man who had been sitting at a table at Chipotle jumped in the 2013 silver Kia Optima and took off. She said she ran after him in the parking lot, screaming at him to give her baby back.
The vehicle fled westbound against traffic, then southbound on Sierra against traffic before heading out of sight.
The theft was reported at 1:56 p.m. Less than 90 minutes later, a Riverside County sheriff's deputy found the vehicle empty in Norco at Bluff Street and River Road.
A witness told the deputy that a man had exited the vehicle with the baby in his arms and ran up a nearby hill. Deputies canvassed the area and found the man with the baby, who was unharmed.
The suspect was arrested. He was identified as 45-year-old Agabosi Christopher Tanpinu. Police say he had been released from jail on bail just a few days earlier on burglary charges.
The baby was checked out at a local hospital and then reunited with her mother.
Police say the woman realizes what a mistake she made. She is not expected to face any charges or citations.