The former two-term New Mexico governor -- who ran for the Republican presidential nomination last year before switching to the Libertarian Party -- should have been allowed to join President Barack Obama and Republican nominee Mitt Romney in the three presidential debates, including the final one Monday night, because he is on the ballot in 48 of 50 states, the former CNN host said.
Michigan and Oklahoma are the only states where Johnson is not on the ballot. The Libertarian also enjoys the support of a few small "super PACs," The New York Times said.
"I would say if you're on the ballot in [that many] states, you should be in the debates," King told Politico as he prepared to moderate the first of two debates among third-party presidential nominees.
Some Republicans told the Times Johnson could be a spoiler in the Nov. 6 election, drawing votes from Romney in a very close election with Obama.
Tuesday night's debate, in Chicago at 8 p.m. CDT (9 p.m. EDT), was to bring together Johnson, Green Party nominee and former Massachusetts gubernatorial candidate Dr. Jill Stein, Constitution Party nominee and former GOP U.S. Rep. Virgil Goode of Virginia, and Justice Party nominee and former Democratic Salt Lake City Mayor Rocky Anderson.
The debate was to be carried live by C-SPAN, al-Jazeera English and RT, or Russia Today, and be streamed live online by Ora TV, Link TV and on the website of debate sponsor Free and Equal Elections Foundation.
It was not to be carried by CNN, Fox News Channel, MSNBC or any of the traditional U.S. broadcast networks.
A second debate, with two of the four candidates, is to take place in Washington Oct. 30, the foundation said Monday.
Viewers of the first debate were to be asked to choose through an online runoff vote, within 24 hours of Tuesday's debate, which two candidates they wanted to advance to the final debate, the foundation said.
The results are to be announced Thursday.
King said he agreed to moderate Tuesday night's debate because he thought smaller-party candidates "deserve a voice."
"It's obvious they're not going to win, but in the Constitution it never says there's a Democrat or a Republican Party," he told Politico. "It never mentions a two-party system. We've had Federalist presidents, Whig presidents. ... We've always had independent candidates. They deserve a voice and they haven't had a voice in this campaign at all."
Debate questions would come from viewers, who were encouraged to submit them before and during the debate through social networks Facebook, Twitter, Reddit or Tout, Free and Equal Elections said.
The hashtag is #AskEmThisLarry. King will choose which questions to ask the candidates. But he told Politico he would jump in if the candidates dodge the issues.
"I'm used to debates, and the moderator has a role," he said. "It's not his show. It's their show. But he's not a potted plant."