Representative Scott Rigell of Virginia says he plans to vote for the Libertarian Party’s presidential ticket, becoming the first member of Congress to express support for Gary Johnson’s third-party campaign.

In an interview on Friday, Mr. Rigell, a Republican, said he had settled on Mr. Johnson, the former governor of New Mexico, as the best option available.

“I’ve always said I will not vote for Donald Trump and I will not vote for Hillary Clinton,” Mr. Rigell said. “I’m going to vote for the Libertarian candidate.”…

Mr. Johnson and his running mate, former Gov. William F. Weld of Massachusetts, have been seeking to woo disaffected Republicans who view Mr. Trump as unacceptable. Should additional Republican officeholders follow Mr. Rigell in backing the third-party ticket, it could help Mr. Johnson gain credibility as an alternative choice.