"As a proud Republican, casting my vote for president has usually been a simple matter. This year is different," she said in a statement released Tuesday night. "To vote Republican out of party loyalty alone would be to endorse a candidacy that I believe has exploited anger, grievance, xenophobia and racial division. Donald Trump’s demagoguery has undermined the fabric of our national character."
The billionaire businesswoman cited a list of controversial positions that Trump has campaigned on, including barring foreign Muslims from entering the country and building a wall between Mexico and the U.S.
She went on to praise Clinton for her "temperament" and "global experience," which Whitman said would make the former secretary of state a "far better choice" for president.
"In a tumultuous world, America needs the kind of stable and aspirational leadership Secretary Clinton can provide. I urge all Republicans to reject Donald Trump this November," she concluded.
Whitman joins a growing list of prominent Republicans who have come out in support of Clinton after a series of controversial statements by Trump.
Rep. Richard Hanna of New York became the first Republican in Congress to say he would vote for Clinton over Trump.
In 2010, Whitman ran an unsuccessful campaign as a Republican for California governor, spending more than $140 million of her own money in the process.