The announcement from the 47-year-old Democrat comes just a few months after he was re-elected to a second four-year term as the state's second-highest elected official. Newsom said last month that he would not pursue a U.S. Senate seat, creating anticipation he would seek the state's top post.
Newsom has been a controversial national figure since 2004 when he ordered the San Francisco city clerk to ignore state law at the time and give marriage licenses to gay couples. Newsom served seven years as mayor.
In an interview Wednesday, Newsom said he will spend the next few years raising money and devising "a grand strategy" to restore California's greatness. He said Gov. Jerry Brown deserves credit for restoring the state's fiscal solvency, and the next step is a vision for its future.
"I want to take the time to do it right. One thing you can't manufacture is time, and you can't get it back. So many mistakes in politics and in campaigns are made because of those constraints," Newsom said. "And I want the opportunity to look out in to the future with a different perspective, with a more sustainable perspective."
Opening a campaign committee nearly four years before the election allows Newsom to begin collecting large checks, boost his name recognition and portray himself as the front-runner. He has more than $3 million remaining in his campaign account for lieutenant governor after cruising to re-election in November.
"He is, I think, trying to clear the field," said Sherry Bebitch-Jeffe, a senior political science fellow at the University of Southern California. "He's going to need to get name recognition. If he's serious, he's made his decision, he wants to run, the earlier he's out there, the more likely he is to gain name recognition."
Other potential Democratic candidates include former Los Angeles Mayor Antonio Villaraigosa, who is said to be weighing a bid for U.S. Senate, and billionaire climate activist Tom Steyer, who opted not to run for Senate.
Newsom launched a brief campaign for governor before dropping out in 2009 as then-Attorney General Brown sought the position. Brown won in 2010 and was re-elected in November.
When asked what he learned from his short campaign against Brown, Newsom said, "Don't ever consider running for office against someone in the state of California with the last name Brown."
Although Newsom praised Brown in his announcement Wednesday, the two are not known to be close, despite a longstanding familial relationship. As governor from 1975 to 1983, Brown appointed Newsom's father to the Superior Court and later to the state Court of Appeals.
Newsom last year became the highest-ranking Democrat to challenge Brown's $68 billion high-speed rail project, saying he no longer backs the bullet train and would like to see the money diverted to more pressing infrastructure needs.
He said Wednesday that hasn't given up on the project and he hopes Brown can solve its problems.Suggest a correction