"Your reputation is amazing. I will not let you down," Trump told Alex Jones during a Wednesday afternoon appearance on the Infowars.com proprietor's show.
Jones shared the love, telling Trump that "my audience, 90% of them, they support you."
Jones, who has advanced a number of conspiracy theories, gained prominence as a 9/11 "truther."
He has previously asserted on his radio show that there is a "98% chance this was a government-orchestrated controlled bombing.
In October, he said on a show that "there is a cover-up," and then highlighted Trump's recent criticism of George W. Bush's handling of 9/11.
Trump has disputed most officials' characterizations of 9/11 too in recent days, arguing that thousands of Muslims in New Jersey celebrated the attacks. The real estate mogul and Republican presidential front-runner tweeted a link to an Infowars.com post supporting his claims.
However, Infowars.com itself in October reported on Trump dismissing a 9/11 truther's question on the campaign trail, quoting him saying: "Is this guy some kind of conspiracy guy?"
Trump also praised libertarianism as "sort of interesting," and said that "there are certain things I really like about it."
His critique of libertarianism comes on the issue of national security, he said.
"If this were 100 years ago, I'd say forget about it ... (But) the weaponry is so powerful and they hate us so much that we have to now protect," Trump said.
Trump also offered his regular criticism of trade deals and a declining economy.
"If you have to suffer through four more or eight more years of what's gone on in the past -- we're beating eaten away," he said. "It's just eating away at our country, and in my opinion, we can make America greater than ever before, but we have to get going."
Both Trump and Jones said that the interview was arranged by Roger Stone, a long-time political operative who was involved in a dust-up with Trump's campaign in August.
Stone, who had been advising Trump, split with his campaign in the wake of Trump's criticism of Fox News host Megyn Kelly. The two sides then bickered over who had fired whom.
Trump's campaign said that it fired Stone, saying that "Roger wanted to use the campaign for his own personal publicity." Stone shot back by telling CNN he "categorically denies" being fired and providing what he said was his resignation letter. He also tweeted that Trump "didn't fire me -- I fired Trump."
On Wednesday, it sounded like the two had cleared the air.
"Well Roger's a good guy and he is a patriot ... He's a tough cookie, I will tell you that. But people like him. But he's been so loyal and so helpful," Trump said, adding that Stone "helped set up this interview."