"I had to put country before party," the CEO of Hewlett Packard Enterprise said on "Squawk on the Street." She said a common refrain from supporters have been: "Thank you for the courage to stand up."
In a LinkedIn post last month, Whitman announced her support of Clinton, writing: "Donald Trump's demagoguery has undermined the fabric of our national character."
Whitman, who ran an unsuccessful 2010 GOP gubernatorial bid in California, believes Democrat Clinton is better for the country and the economy.
On Thursday, Whitman cited Clinton's infrastructure plans, focus on small business, and skills training program, while slamming Trump's candidacy.
"When I travel outside the United States — heads of state, business leaders — they actually are terribly, terribly worried about Donald Trump as a president," she said.
Another business leader threw his support behind Clinton on Wednesday evening.
Starbucks Chairman and CEO Howard Schultz endorsed Clinton for president on CNBC's "Mad Money." Schultz, who had once been seen as a possible candidate himself, also said he's still not running for the White House.
Trump does have his deep-pocketed supporters. For example, billionaire Wilbur Ross, a senior policy advisor to the Trump campaign, told CNBC's "Squawk Box" last month the real estate mogul has the right idea on trade, and his economic plan would help stem the overseas exodus of American jobs.