Six shots were fired at 10:50am (6:50pm BST) outside a Catholic Charities building in central Fresno, with two people later dying on the scene.
A third person later died in hospital after what police Chief Jerry Dyer branded as an act of random violence.
39-year-old suspect Kori Ali Muhammad has been apprehended by police following the attack.
Witnesses claim the gunman, carrying a large handgun, was cursing as he reloaded and fired rounds into the street.
Two of the victims are believed it be clients of the charity, while the third is believed to be a gas and electric worker.
It comes after unarmed 25-year-old security guard Carl Williams was killed after being shot multiple times at a Motel 6.
Kori Ali Muhammad was named as the prime suspect in the case, just three days before his arrest.
At the time police claimed Muhammad was a homeless man known to frequent the area and should be treated as armed and dangerous.