O'Rourke is facing current Republican Texas Governor Greg Abbott in a bid for governor, who he slammed as a "thug" in his SXSW discussion.
"He's a thug, he's an authoritarian," O'Rourke said of Abbott on Saturday.
"We've gotta get past this guy, this extremism, these fringe politics that are so deeply hurting people in the state of Texas," O'Rourke said of Abbott.
O'Rourke also accused Abbott of having a "crazed fixation" on transgender children, saying that the governor was failing to bolster resources and protections for sex-trafficked children.
"Those same kids who were rescued from sex traffickers, are now being trafficked for sex by their guardians in the state of Texas," O'Rourke claimed. "The governor knew there was a problem for four months, and he did not do sh--."
O'Rourke, a former Democratic candidate in the 2020 Democratic presidential primary, is running for governor of Texas and sailed through his party's primary at the start of the month.
The gubernatorial candidate also took Abbott to task at SXSW for the state's unpreparedness for the winter power outages that swept across the state last year.
"The lights went out, and the heat failed. And the water stopped flowing because the pipes froze as well. And people lost their lives as a consequence," O'Rourke said, going on to accuse Abbott of being in bed with gas companies unwilling to invest in weather-proofing the state's energy infrastructure.
However, pressed for proof on the "straight line" connections between Abbott and energy companies – specifically Energy Transfer Partners, with CEO Kelcy Warren – O'Rourke softened his rhetoric a bit.
"The facts that I laid out, I think, stand for themselves. And folks are welcome to come to different conclusions if they want to," O'Rourke said. "But I think we have a very clear case of a governor who stands with the corporations and the high-dollar donors."
O'Rourke is currently involved in a lawsuit filed by Warren for defamation over claims that O'Rourke "falsely accused" him of "extortion" and "bribery," according to court documents.
"[Warren] is getting filthy, illegally rich off the natural resources of this state, and then charging us a premium 200 times the going rate just to stay warm in our own homes when the temperature drops," O'Rourke said.
"And Abbott instead of holding his responsible and accountable and getting that money back -- and ensuring that he serves some time or there is some justice for what he has done to the people of Texas --takes a one million dollar campaign contribution from him."
Fox News has reached out to Abbott for comment on O'Rourke's statements Saturday.
In an extremely close race, O’Rourke narrowly lost his run for U.S. Senate against Sen. Ted Cruz in 2018, prior to his failed 2020 presidential bid.
O'Rourke made national headlines with declarations like "hell yes, we are going to take your AR-15" in his campaign, which he has since softened.
The Democrat said earlier this year that he has "no interest in taking" assault weapons from gun owners, a total walk-back of his previously brazen and unpopular statements on Texas gun laws.
"I’m not interested in taking anything from anyone," O’Rourke reportedly said to reporters in Tyler, Texas. "What I want to make sure that we do is defend the Second Amendment. I want to make sure that we protect our fellow Texans far better than we’re doing right now."
He doubled down on those comments during his SXSW remarks, not directly committing to taking guns out of the hands of owners.
O'Rourke also became one of the first prominent Democrats to publicly state opposition to the teaching of critical race theory in schools Friday.
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Fox News' Jessica Napoli, Rémy Numa and Houston Keene contributed to this report.
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