Officers responded to the scene in the 8100 block of Foothill Boulevard, near the intersection of McVine Avenue, just before 1 a.m. after someone reported what appeared to be a person sleeping in their car in the driver's seat.
When first responders arrived, the man was unconscious, not breathing, and suffering from a gunshot wound to his head. He was pronounced dead at the scene by the Los Angeles Fire Department.
The victim's name has not been released and is described as a 51-year-old man from Palmdale.
A weapon was not discovered in the car and a description of a potential suspect was not available. Detectives were canvassing the area for surveillance video, witnesses, and additional evidence.
Anyone with information is asked to call LAPD Valley Bureau Homicide at 818-374-1925. Those who wish to remain anonymous can submit tips online.
FOX 11's Kelli Johnson contributed to this report.