[1] He assisted Clarence Thomas in his Supreme Court confirmation hearings and led campaigns to support the nominations of John Roberts, Samuel Alito, Neil Gorsuch, Brett Kavanaugh, and Amy Coney Barrett.

[6] When Leo was five years old, his mother married an engineer, and the family moved to Monroe Township, New Jersey, where he spent most of his childhood.

[8][6] Leo attended Cornell University,[4] graduating with a bachelor's degree in 1986, working as an intern in the office of Senator Orrin Hatch.

[4] Leo took leaves of absence from the Federalist Society to assist the Bush administration's judicial nomination and confirmation efforts.

[4][10][11] In 2017, legal analyst Jeffrey Toobin wrote that Leo was "responsible, to a considerable extent, for one third of the justices on the Supreme Court".

"[4] In 2016, Leo worked with Senate Majority Leader Mitch McConnell to block President Barack Obama's replacement appointee, Merrick Garland.

[17][4][18] In 2018, Politico reported that Leo had personally lobbied for Brett Kavanaugh's nomination for the Supreme Court seat vacated by Anthony Kennedy, raising upward of $15 million in support of his confirmation.

[21][22] Defunct Newspapers Journals TV channels Websites Other Congressional caucuses Economics Gun rights Identity politics Nativist Religion Watchdog groups Youth/student groups Miscellaneous Other Media outlets have described Leo as the "behind-the-scenes leader of a network of interlocking nonprofits that has raised and spent hundreds of millions of dollars to support conservative judges and causes".

[25][27] An October 2022 article by Kenneth P. Vogel in The New York Times detailed how Leo, who had been best known for his role in conservative judicial appointments, developed a larger coalition on the right.

In January 2020, Leo announced that he would be leaving his position as vice president at the Federalist Society to start a new for-profit group, CRC Advisors, a conservative political consulting firm.

[29] Vogel wrote that Leo had built "one of the best-funded and most sophisticated operations in American politics, giving him extraordinary influence as he pushes a broad array of hot-button conservative causes and seeks to counter what he sees as an increasing leftward tilt in society.

"[31] Teneo (from Latin, meaning "I hold" or "I grasp") says it has a plan to "crush liberal dominance" in journalism and education, as well as in business and politics;[32] it consists of various loosely affiliated non-profit and for-profit entities, which collectively spent nearly $504 million between mid-2015 and 2021.

[30][1] The Teneo Network is a member of the advisory board of Project 2025,[33] a collection of conservative and right-wing policy proposals from the Heritage Foundation to reshape the United States federal government and consolidate executive power should the Republican nominee win the 2024 presidential election.

"[23] In June 2023, ProPublica reported that Leo helped organize and attended a fishing trip with Justice Samuel Alito and businessman Paul Singer, whose firms later were parties to litigation before the Supreme Court.

[36] In March 2023, Politico reported that in 2021 and 2022, Leo had moved at least $43 million from his nonprofits into CRC Advisors, a for-profit business which he chairs.

[43][44] After he met with leaders of a New England fisherman stewardship association opposed to offshore wind projects, the Concord Fund donated $573,000 to the group in both 2023 and 2024.

[51] He has been a US delegate to the United Nations Council and the UN Commission on Human Rights, as well as the Organization for Security and Cooperation in Europe and World Health Assembly.