Police received a call of a possible shooting in the 200 block of Devonshire Court at about 10:06 p.m. Friday.
Once there, officers determined that multiple shots had apparently been fired from a vehicle in the direction of people who were in front of a home.
Police and emergency responders found the 21-year-old victim who was struck by the gunfire and pronounced him dead at the scene.
His name is being held until family members are notified, police said.
No other injuries were reported.
Witnesses told police they saw a possible suspect vehicle -- a blue Saturn Vue with several occupants -- speeding away from the area immediately after the gunfire.
Police continue to investigate the shooting and are asking anyone with information about the incident to contact the Pleasant Hill Police Department at (925) 288-4630.