Jack Michael Posobiec III (/pəˈsoʊbɪk/ pə-SOH-bik; born December 14, 1984) is an American alt-right political activist, television correspondent, conspiracy theorist, and former United States Navy intelligence officer.

Posobiec is known for his pro-Donald Trump comments on Twitter. As of 2016, he was using white supremacist and antisemitic symbols and talking points, including references to the white genocide conspiracy theory. In 2017, he promoted fake news, including the debunked Pizzagate conspiracy theory claiming high-ranking Democratic Party officials were involved in a child sex ring. Also in 2017, Posobiec distanced himself from white nationalism and expressed opposition to "hate groups and bigotry".

He was a promoter of the Stop the Steal movement in the wake of the 2020 election cycle. From 2018 to 2021, Posobiec was employed by One America News Network (OANN), a far-right cable channel, as a political correspondent and on-air presenter. He left OANN in May 2021 to begin hosting a show for the conservative student organization Turning Point USA, and to join conservative news site Human Events as a senior editor.

Posobiec was born and raised in Norristown, Pennsylvania, to a family of Polish descent. His parents were both Democrats.

He attended Kennedy–Kenrick Catholic High School and college at Temple University. While at Temple, he became the chairman of the Temple University College Republicans and started a chapter of Students for Academic Freedom, an organization run by the David Horowitz Freedom Center. He was a summer intern for US Senator Rick Santorum and volunteered for US Representative Curt Weldon's unsuccessful reelection campaign in 2006. He graduated from Temple in 2006 with a double major in political science and broadcast journalism.

After graduation, Posobiec worked for the United States Chamber of Commerce in Shanghai, People's Republic of China. He performed a minor role in the film The Forbidden Kingdom, which was released in 2008. He later worked for the conservative talk radio station WPHT and then for the campaign of Steve Johnson in the 2010 Pennsylvania lieutenant gubernatorial election. Posobiec served several years in the United States Navy Reserve from 2010 to 2017, reaching the rank of lieutenant junior grade. He was deployed for ten months at Guantanamo Bay Naval Base from September 2012 and worked at the Office of Naval Intelligence (ONI), where he later worked again as a civilian.

During the 2016 election, Posobiec was a special projects director of Citizens for Trump, a pro-Trump organization but not an official group. In March 2017, Posobiec resigned from his full-time civilian position at ONI, saying that his support for Trump led to a "toxic work environment". As of August 2017, his security clearance was suspended and was under review.

Posobiec describes himself as a "Republican political operative". During the 2016 election, Posobiec was a special projects director of the political organization Citizens for Trump. Semafor found he was by far the most influential voice with dozens of Republican strategists going into the 2024 campaign season.