Schwarzenegger was not swayed by pleas from Hollywood stars and petitions from more than 50,000 people who said that Williams had made amends during more than two decades in prison by writing a memoir and a series of children's books about the dangers of gangs.
"After studying the evidence, searching the history, listening to the arguments and wrestling with the profound consequences, I could find no justification for granting clemency," Schwarzenegger said in writing less than 12 hours before the execution. "The facts do not justify overturning the jury's verdict or the decisions of the courts in this case."
With a reprieve from the federal courts considered unlikely, Williams was set to die by injection at San Quentin State Prison early Tuesday for murdering four people in two 1979 holdups.
Just earlier Monday, the 9th U.S. Circuit Court of Appeals rejected a stay of execution for Williams.
After a campaign by death penalty opponents and Hollywood stars that made him one of the nation's biggest death-row cause celebrities in decades.
Williams was condemned in 1981 for gunning down a clerk in a convenience store holdup and a mother, father and daughter in a motel robbery weeks later. Williams claimed he was innocent.
Over the years, the case has been reviewed by courts at every level, and the verdict has been upheld every time, reports CBS News correspondent Steve Futterman.
The state's high court on Sunday unanimously ruled, 6-0, saying the last-minute appeal lacked merit and was untimely as well. The appeal said, among other things, that Williams should have been allowed to argue at his murder trial that someone else killed one of his four alleged victims.
The justices had turned down another appeal from Williams days earlier.
Immediately after the decision, Williams' lawyers filed a virtually identical petition with the 9th U.S. Circuit Court of Appeals in San Francisco. A decision was expected Monday.
There aren't a whole lot of legal issues to consider when a case gets down to the clemency stage, says CBSNews.com Legal Analyst Andrew Cohen. At that point, the issue is as much political as it is legal because of course there is no appeal from a clemency ruling. So Williams' last best chance is in federal court and he hasn't had much success there, either.
Prosecutors and victims' advocates contended Williams was undeserving of clemency because he did not own up to his crimes and refused to inform on fellow gang members. They also argued that the Crips gang that Williams co-founded in Los Angeles in 1971 is responsible for hundreds of deaths, many of them in battles with the rival Bloods for turf and control of the drug trade.
Williams stood to become the 12th California condemned inmate executed since lawmakers reinstated the death penalty in 1977 after a brief hiatus.
Defense attorneys eagerly awaited Schwarzenegger's decision on whether to grant Williams clemency. They have asked the governor to spare the condemned man's life with the claim that Williams, who has written several children's books extolling the evils of gang life, has redeemed himself during 24 years at San Quentin State Prison.
"We are awaiting the governor's position on clemency," Williams' clemency attorney Jonathan Harris said.
Schwarzenegger has not granted clemency to two other prisoners since he was elected in 2003, but said last week he was agonizing over what to do in the Williams case. The last time clemency was granted in California was back in 1967, when Ronald Reagan was governor, reports CBS News' Teri Okita. Since the death penalty was reinstated in 1977, 11 inmates have been put to death.