Whitman's campaign confirmed the contribution to The Associated Press on Monday, although it had not yet appeared in financial statements filed with the secretary of state's office.
The billionaire last week won the Republican primary for governor, allowing her to challenge Democrat Jerry Brown in the November general election. Her campaign has spent more than $81 million so far, a record for a California primary.
Brown has spent just $400,000 and has upwards of $20 million in the bank.
Following her primary victory Whitman talked about her personal wealth - spinning it this way. "People ask me all the time, 'Can elections be bought?' The answer is, elections can't be bought, but candidates can and Jerry Brown is bought and paid for by the unions."
Brown's stump response to her wealth: "It's not enough for someone rich and restless to look in the mirror one morning and decide, 'I want to be governor of California.' We tried that. It didn't work," Brown says referring to Gov. Arnold Schwarzenegger.