Officers found the body inside the vehicle on the 1600 block of East Kingsley Avenue around 2:45 a.m.
He suffered multiple gunshot wounds to the torso and died as a result of his injuries.
The victim's vehicle was described as a gold 1999 Lexus SUV.
The motive remains unknown. No arrests have been made.
The investigation is ongoing. Anyone with information regarding the incident was urged to contact Pomona police at (909) 620-2085.