"I would rather ask questions to people in positions of power instead of speaking on their behalf," King said in the ad.
"That's why you can find my show Larry King Now right here on RT."
RT said the longtime CNN host would host "a mold-breaking political talk show" from next month, "speaking to both leading establishment figures and those who are not afraid to go against the grain."
"The veteran broadcaster will not shy away from causing controversy, or using his authority to give a chance to hear voices other media ignore," RT said on its website rt.com.
Despite that claim, the 79-year-old master of the softball interview is unlikely to make waves in Russian domestic politics.
Independent journalists, opposition politicians, NGO leaders and businessmen have been systematically cowed -- or beaten or killed in dozens of cases -- during President Vladimir Putin's more than decade in power, with the television sector coming under especially tight control.
The lavishly funded Russia Today chiefly aims to project the Kremlin viewpoint abroad and has little impact inside the country.
RT said it would be airing a new show "Politics with Larry King" from June and also hosting "Larry King Now," which has run on Hulu since July 2012. The programs will be recorded in Washington, DC, and Los Angeles.
Simonyan said King's record at CNN, where he hosted the Larry King Live show from 1985 and 2010, showed he was "a terrific fit for our network."
"Whether a president or an activist or a rock star was sitting across from him, Larry King never shied away from asking the tough questions," she said on rt.com.
The English-language RT network was formed in 2005 and won attention for broadcasting a controversial show by WikiLeaks website founder Julian Assange.
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