The jury also found special circumstances of multiple murder that make Ng eligible for the death penalty, to be determined in a separate penalty phase of the trial.
Ng, a 38-year-old native of Hong Kong, had been charged with killing seven men, three women, and two baby boys in 1984 and 1985.
One count, No. 4, was dropped by the judge earlier Wednesday, after jurors pronounced themselves deadlocked on it. That count involved the death of Paul Cosner.
Ng looked down at the defendants' table as the verdicts were read and showed no reaction.
Court clerk Terri Walsh read out the verdict for each count, saying: "We, the jury, in the above entitled case find the defendant, Charles Chitat Ng, guilty of first-degree murder."
The series of killings grabbed national headlines in the mid-1980s. Ng's female victims were tortured and raped after being lured to the home of Leonard Lake, about 150 miles east of San Francisco in the Sierra Nevada foothills. Lake killed himself by swallowing cyanide in June 1985.
Ng headed for Canada, where he was arrested on a fugitive warrant in 1985 while camping at a park on the outskirts of Calgary. Authorities searching his hideout found a stun gun, a pistol, handcuffs, and victims' belongings.
Incarcerated in Edmonton Penitentiary, Ng was placed in a cell next to informant and career criminal Maurice Laberge. The two collaborated drawing gruesome cartoons, passing them under a door, Ng testified.
Laberge testified against Ng at an extradition hearing, alleging Ng told him details about the murders only the killer could have known.
The extradition dragged on for six years in Canada, which has no death penalty and has reservations about sending fugitives to possible execution in other countries.
When he was returned to California, his attorneys argued that extensive news coverage made a fair trial impossible in Calaveras County. The case was transferred to Orange County in 1994.
By Larry Gerber