The Associated Press called the race shortly after 8:30 p.m.
Whitman, the billionaire former eBay chief executive who poured tens of millions of her own fortune into her first-time bid for political office, easily won the Republican primary for California governor Tuesday, advancing to face a Democratic icon, former two-term Gov. Jerry Brown, who secured his party's nomination on Tuesday, too.
Whitman, 53, worked on the presidential campaigns of Mitt Romney and John McCain. She has spent much of the primary in tightly scripted appearances and was criticized early on for avoiding detailed questions from political reporters.
The opponent Whitman beat Tuesday, state Insurance Commissioner Steve Poizner, is a wealthy Silicon Valley entrepreneur who spent $25 million of his money on his race.
With 22 percent of precincts reporting, Whitman had 63 percent of the vote compared to Poizner's 27 percent.
"I am battle-tested and I'm ready to give Jerry Brown the toughest election fight he's faced in his 40 years of politics," Whitman told raucous supporters at a hotel in Universal City. The group erupted in cheers, waved the state flag, and screamed "We want Meg! We want Meg!"
Poizner conceded defeat, but hedged on whether he would throw his support to Whitman who holds more moderate views.
"If Meg Whitman runs on conservative principles, she deserves our full support," he said.
The heated battle with Poizner to win over conservative GOP primary voters forced Whitman to move to the right on issues such as abortion and illegal immigration, moves that could hurt her against Brown in November.
Democrats and moderate independents comprise two-thirds of the electorate in California. Without a serious primary challenger, Brown has positioned himself as a moderate, pledging not to raise taxes and to make the kind of spending cuts that Whitman also campaigned on.
The gubernatorial race promises to be the most expensive in state history.
Whitman has already spent more than $81 million on her primary race, all but $10 million of it her own, far outpacing any previous primary contest in California. She had previously said she would spend $150 million in all on her gubernatorial bid, but has declined in recent weeks to say whether that number is now higher.
Earlier on Tuesday, a confident Whitman was practicing her acceptance when a San Francisco Chronicle reporter recorded her teleprompter speech.
Whitman proclaimed "Thank you so much ... What a great night! This victory is yours! I just received a very gracious phone call from Steve Poizner conceding the race.” The Chronicle reporter captured the whole thing using a small camera.
It can be viewed on the San Francisco Chronicle website.
NBCLA reporter Conan Nolan covering the Whitman victory party reported that she planned on accepting the nomination before Poizner concedes. The very first poll results released Tuesday night showed Whitman leading Poizer about 2-1.