“Our nation faces a unique set of challenges that require steady and experienced leadership," Westine said in a statement. "That is why today I am personally supporting Hillary Clinton.
"She has the expertise and commitment to American values to grow the economy, create jobs and protect America at home and abroad," she said.
Westine did not say why she would not support Trump.
She joins a growing list of conservatives in the business, foreign policy and political spheres who have come out in support of Clinton.
On Sunday, the political director in the Reagan administration — Frank Lavin — wrote in a commentary for CNN that he could not support Republican nominee Donald Trump and would vote for Clinton instead.
"Trump falls short in terms of the character and behavior needed to perform as president," Lavin wrote. "This defect is crippling and ensures he would fail in office."
On Friday, Michael Morell, a former acting CIA director — who served in both Republican and Democratic administrations — wrote a scathing denunciation of Trump in his endorsement of Clinton.
Moderate Republican Rep. Richard L. Hanna of New York, also endorsed Clinton.
Westine, the former Bush administration official, is currently the president and chief executive of the Personal Care Products Council and is the former president and chief executive of TechNet, a political network of high-tech chief executives.