The man, 21, died at about 3 p.m., the coroner's bureau said. A second man was shot in the Saturday morning incident but is expected to survive.
The Union City Police Department received a 911 call just before 1 a.m. saying gunshots had been fired and two men were injured at 33558 Fourth St.
When officers arrived, they found two men with gunshot wounds. Both victims received emergency medical aid from paramedics and were later transported to an area hospital.
One victim, a 21-year-old Union City man, died that afternoon. The second man, a 33-year-old Union City resident, is expected to recover from his injuries.
Anyone with information about the shootings is asked to call Detective Stan Rodrigues at (510) 471-1365.