The incident happened early Monday morning at an apartment complex on Alexander Avenue near G street.
A resident called 911 after authorities say he interrupted the theft in progress.
The car had been lifted by a jack and at some point, it came down on top of the suspect.
First responders worked to get the man out from underneath the vehicle and tried to save him, but he died from his injuries.
Merced police found several tools tied to stealing catalytic converters underneath the car.
The man who died has not yet been identified.