Former Vice President Dick Cheney, one of the most influential and hawkish conservatives in the modern Republican Party and a figure reviled by the left, said Friday he would be voting for Vice President Kamala Harris because he regards former President Donald J. Trump as a grave danger to the country.

“In our nation’s 248 year history, there has never been an individual who is a greater threat to our republic than Donald Trump,” Mr. Cheney, 83, said in a statement. After Mr. Trump’s actions trying to steal the 2020 presidential election and then using “lies and violence” to keep himself in power, Mr. Cheney said, “he can never be trusted with power again.”

The former vice president added: “We have a duty to put country above partisanship to defend our Constitution. That is why I will be casting my vote for Vice President Kamala Harris.”

Mr. Cheney released his statement after one of his daughters, former Representative Liz Cheney, the once high-ranking Republican from Wyoming who sacrificed her political career by breaking forcefully with Mr. Trump after the Jan. 6, 2021, attack on the Capitol, said this week that she would be voting for Ms. Harris.

On Friday during a panel discussion at the Texas Tribune Festival in Austin, Ms. Cheney revealed that her father, an unapologetic partisan, would be, too.

“Dick Cheney will be voting for Kamala Harris,” Ms. Cheney said, a remarkable statement that the Cheneys themselves could not have foreseen making even four years ago.