Constable Wayne Burnett said he was "shocked and appalled" to discover the driver's priorities when he pulled the vehicle over on a highway south of Alice Springs.
The 30 cans of beer were buckled in while the child sat on the floor.
"I haven't ever seen something like this before," he said.
"There were four adults in the car, two in the front seat and two in the back seats and in between those adults there was the carton of beer strapped in with the belt," he said.
"The child was sitting in the lump in the centre, unrestrained."
The driver was fined 750 dollars (£360) for driving an unregistered and uninsured vehicle and failing to ensure a child was wearing a seatbelt.