Whitman congratulated Fiorina on Tuesday night in a victory speech in the city of Los Angeles.
"Career politicians in Sacramento and Washington DC be warned: You now face your worst nightmare, two businesswomen from the real world who know how to create jobs, balance budgets and get things done," Whitman said.
Whitman had worked on the presidential campaigns of Republican candidates Mitt Romney and John McCain in 2008.
She now advances to compete for the governor position against candidate Jerry Brown, an icon of the Democrat party who had served as a governor for California from 1975 to 1983, the mayor of Oakland from 1999 to 2007 and an attorney-general in 2007.
The two will compete to replace Arnold Schwarzenegger, the current governor.
Whitman, a billionaire businesswoman, has already spent more than $71 million out of her own fortune on her campaign.
She helped make the race for governor this year the most expensive contest in US history outside of a presidential election.
Like Whitman, Fiorina is a novice in the political arena who also took part in the 2008 presidential contest, but as an economics adviser to McCain.
During the primary, Fiorina appealed to conservative voters with her views
on laws of abortion, guns and gay marriage.
She also touted an endorsement from Sarah Palin, the former vice-presidential candidate.
The primary came as public confidence in government falters in the most populous US state, which is facing record 12.6 per cent unemployment and a $20bn budget deficit.
Al Jazeera's Rob Reynolds, reporting from Los Angeles, said the outcome of the primaries could have a major impact on the political agenda of Barack Obama, the US president.
"All across the country, not just in California, but everywhere there has been a strong anti-incumbent mood among the electorate," he said.
"Many people are angry about what is happening in Washington, so it could very well mean that Obama's Democratic party, which controls the congress, could suffer big losses in November's elections.
"If that happens, it means the Republicans will be stronger than the opposition party and that president Obama will have much more difficulty passing and enacting any large-scale new initiatives, for example, immigration reform."