The outgoing congressman wrote in an op-ed in The Syracuse Post Standard that he differs with Clinton on a number of policies but that Trump "is unfit to serve our party and cannot lead this country."
"While I disagree with her on many issues, I will vote for Mrs. Clinton," Hanna wrote.
"I found [Trump] profoundly offensive and narcissistic but as much as anything, a world-class panderer, anything but a leader," he wrote. "Little more than a changing mirror of those he speaks to. I never expect to agree with whoever is president, but at a minimum the president needs to consistently display those qualities I have preached to my two children: kindness, honesty, dignity, compassion and respect."
"In his latest foray of insults, Mr. Trump has attacked the parents of a slain U.S. soldier. Where do we draw the line?" Hanna asked.
In March, Hanna said he would never vote for Trump.