Richard Grenell, who is openly gay, joined Mr Romney's campaign late last month.
The Huffington Post reported that Mr Grenell, who was working as Romney's foreign policy and national security spokesman, felt like his reputation was being destroyed by far right criticism that he would advocate for gay marriage inside a Romney White House.
"My ability to speak clearly and forcefully on the issues has been greatly diminished by the hyper-partisan discussion of personal issues that sometimes comes from a presidential campaign," Mr Grenell said in a statement.
His employment in the Romney presidential campaign was heavily questioned by Bryan Fischer of the American Family Association, who said Mr Grenell posed a national security risk because of his sexual orientation, reported the Daily Mail.
Mr Grenell resigned after less than a month on the job and cited 'personal reasons' as the cause for his departure.