Norristown police and prosecutors said officers responded to a report of gunshots at about 4:40 p.m. Tuesday.
Borough police found 24-year-old Paul Brown in the driver's seat of a sedan in a rear alley.
Officials say he was taken to Mercy Suburban Hospital and later pronounced dead.
The Montgomery County coroner's office says he died of multiple gunshot wounds and ruled the case a homicide.
Police are asking anyone with information about the slaying to call local police or county detectives.