The body was found about 10:45 a.m. at Golden Valley Road and Robert C. Lee Parkway, according to the Los Angeles County Sheriff's Department.
A deputy on patrol noticed the blue Honda Accord parked illegally on the road shoulder about 9:30 a.m., sheriff's Deputy Crystal Hernandez said.
The car was still there more than hour later, and while preparing to have the vehicle towed, the deputy began an inventory search of the Honda, Hernandez said.
That's when the body was found, she said.
Homicide detectives investigating the fatality told reporters at the scene the body was in the car's trunk.
The crime scene was not far from Golden Valley High School, north of Sierra Highway.
A resident first noticed the car Saturday night, according one report.