Newsom said city halls around the state should be open extended hours throughout the weekend whenever possible.
"The key is that everyone understands that this is not optional," Newsom said. "Counties need to begin immediately providing these certificates without regard to gender immediately."
The 9th Circuit Court of Appeals lifted its stay on an injunction that ordered state officials to stop enforcing California's Proposition 8, which banned gay marriage. With the court's action, counties can now begin issuing same-sex marriage licenses.
A spokesman for the U.S. 9th Circuit Court of Appeals had originally said it would takes the court at least 25 days to act after a Supreme Court ruling.
Opponents of same-sex marriage have argued that Chief U.S. District Judge Vaughn Walker's 2010 decision overturning Proposition 8 applied only to the two same-sex couples who challenged the ballot measure. But the opponents' enthusiasm for going to court to try to narrow the effect of the decision appeared to wane in the hours after the decision.
With Brown and Harris pledging to block Proposition 8 across California, the momentum for gay marriage was likely to hinder any further challenges.
California voters passed Proposition 8 in 2008, six months after the California Supreme Court ruled that gays had the right to wed. The state high court later ruled that the initiative was a valid state constitutional amendment but upheld the validity of an estimated 18,000 same-sex marriages that occurred before the election.
The Supreme Court ruled that ProtectMarriage, the sponsors of Proposition 8, lacked legal authority or standing to appeal Walker's ruling blocking the ballot initiative. The high court said Proposition 8's sponsors were not directly affected by Walker's ruling. Only state officials had the right to appeal, and they refused. That procedural decision wiped out the 9th Circuit Court of Appeals' 2-1 ruling against Proposition 8, leaving only Walker's decision in place and affecting only California.
County clerks who preside over marriages said they were ready for same-sex weddings. Marriage licenses already are gender-neutral, and clerks began receiving calls Wednesday from gay couples wanting to schedule appointments.
Harris called on the 9th Circuit on Wednesday to lift its hold on Walker's ruling immediately. The attorney general said she believed that the appeals court had the authority to act quickly.