Charlie Kirk, a conservative wunderkind who through his radio show, books, political organizing and relentless speaking tours became a close ally of President Donald Trump and did much to shape the hard-right movement that coalesced around him over the last decade, died of a gunshot wound on Wednesday in Orem, Utah, where he had been speaking at a college campus event. He was 31.

President Trump confirmed the death on his social media site, Truth Social.

Mr. Kirk had just taken the stage at the event, at Utah Valley University, when he was shot in the neck shortly after noon.

Mr. Kirk was only 18 when, in 2012, he founded Turning Point USA, which he conceived as a conservative response to liberal organizing platforms like MoveOn.org. He attracted significant early support from Republican donors like Foster Friess and Trump family members like the president’s son Don Jr., who were attracted by his fresh face and bold pitch for gaining ground among young voters.

He quickly became a fixture in the Trumpian media sphere. He tweeted relentlessly, and with a brash right-wing spin, unencumbered by inconvenient facts. Even some conservatives found his approach distasteful, but not Mr. Trump: One mark of Mr. Kirk’s ascendence was how often Mr. Trump retweeted him.

By the start of the first Trump administration in 2017, Mr. Kirk was already in regular rotation on the conservative TV pundit circuit and an in-demand speaker among right-wing organizations.

He was far from the only young face in the emerging Trump movement. But whereas activists like Nick Fuentes and Milo Yiannopoulos went too far, too early in their embrace of baldly racist and homophobic ideas, Mr. Kirk proved preternaturally polished, able to tack quickly among far-right activists, establishment Republicans and skeptical young voters.

He focused his activism on what he characterized as rampant Marxism and gender ideology on college campuses. He encouraged students to report professors whom they suspected of embracing such ideas, and did the same in appealing to parents and grade school students.

He rose even further during the early days of the pandemic, when he was quick to attack the World Health Organization — which, in his typical fashion, he called the “Wuhan Health Organization” — for hiding the source of the Covid-19 virus and claimed that it had emerged from a Chinese lab in the city of Wuhan. He later rallied opposition to school lockdowns and mask mandates.

Mr. Kirk was so vocal in his willingness to spread unsupported claims and outright lies — he said that the drug hydroxychloroquine was “100 percent effective” in treating the virus, which it is not — that Twitter temporarily barred him in early March 2020. But the move only added to his notoriety and seemed to support his claim that he was being muzzled by a liberal elite.

Following the 2020 election, Mr. Kirk led a “Stop the Steal” protest in Phoenix and promised to send 80 “buses of patriots” to Washington on Jan. 6, 2021, to support the outgoing President Trump. Only about seven buses arrived.

A full obituary will appear soon.