The 91-year-old Carter spoke with The Associated Press on the site of a Habitat for Humanity construction project in Memphis.
Carter, considered a worldwide ambassador for Habitat for Humanity, said he doesn't like to advocate for particular issues because he works equally with Republicans, Democrats and people of many religious beliefs in his role with the home building charity.
But he did say that "everybody knows that I'm a Democrat, and I'll be voting Democratic."
Clinton, a former first lady and Secretary of State, is running against Republican billionaire businessman Donald Trump. Polls have shown that Clinton is unpopular with voters, Trump even more so.
"It's been an exciting and unprecedented kind of campaign this year, and unfortunately, the way it's turned out, both choices in the major parties are quite unpopular," Carter said. "But I don't have any doubt that one of the candidates is better qualified than the other."
Carter, who has battled cancer in the past year, is being joined by about 1,500 volunteers during a weeklong effort to build 19 homes in a low-income neighborhood near the city's downtown. The former president wore blue jeans, a hard hat, a tool belt and a red bandanna around his neck as he hammered nails into the wooden frame of a house under construction.
Moving amid the skeleton framing of the house, Carter appeared energetic and sure-footed as he talked with workers and used a level to make sure wooden beams were installed correctly.
Carter revealed in August 2015 that he had been diagnosed with melanoma that spread to his brain. He said in March that he no longer needs cancer treatment. He addressed his health during a news conference, seated beside his wife, Rosalynn.
"Now I feel pretty certain about my cure and the cancer being in remission, but the doctors are still keeping an eye on me," he said.
But during the peak of his fight with the illness, he had his doubts.
"A year ago, I didn't think I was going to live but two or three weeks because they had already removed part of my liver because I had cancer there," Carter said. "After that, when they did an MRI, they found four cancer places in my brain so I thought I just had a few weeks to live."
By last November, Carter was responding to treatment and was able to travel to Memphis for another Habitat for Humanity project.
"By the time I got to here, I was putting on a kind of a false optimistic face," Carter said.
Before a question and answer session during the news conference, Carter drew laughs when he mentioned Trump.
"We'll have questions later. Anybody who asks about Donald Trump will be disqualified from the occasion and will have to leave," Carter said. "So, I just want to give that one premise for the question and answer period. We want to stick to Habitat, if you don't mind."
Jonathan Reckford, CEO of the Atlanta-based charity, said Carter and his wife have donated their time to help build and improve 3,944 homes in 14 countries.
Carter said he plans to go to Canada to build homes with the charity next year. He still teaches Sunday school classes in his hometown of Plains, Georgia.
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