Officers said the gunshot was self-inflicted.
The man was discovered in his vehicle on Michigan Avenue and Schlaff around 3 p.m on Sunday.
A news release from the Dearborn Police Department said the driver was a 32-year-old man and had been observed slumped over his steering wheel when they arrived.
The man later succumbed to his injury after being taken to a local hospital.
Detectives from the department gathered evidence and canvassed the area for potential witnesses before determining the man had shot himself.
"This is a tragic situation and our condolences go out to the family of the deceased," said Dearborn Police Chief Ronald Haddad.
The information is preliminary is the case remains under investigation.