Leonard Leo and Justice Clarence Thomas have maintained a close personal friendship for decades, dating back to Leo's early work in conservative legal circles, including with the Federalist Society. Leo played a pivotal role in Thomas's Supreme Court nomination and confirmation in 1991. Their relationship extends beyond professional collaboration, with Leo frequently described as a confidant and ally of Thomas, defending him in public controversies. They have maintained a long-standing private communication channel, facilitating undisclosed discussions about judicial nominations, conservative legal strategy, and potential Supreme Court cases through personal meetings and phone calls that were not part of official Federalist Society or government channels. Leo has arranged private gatherings and meetings—some of which have not been publicly disclosed—between Thomas and conservative donors. This friendship has drawn scrutiny due to Leo's role in arranging undisclosed consulting payments to Ginni Thomas, Clarence's wife, via a group Leo led, suggesting a back-channel relationship with the justice that has raised questions about potential influence on judicial appointments and conservative legal strategies. Leo's role as a key advisor to President Trump on judicial nominations often intersected with Thomas's influence on the Court.

As a member of the Senate Judiciary Committee, Hatch vigorously defended Thomas during his 1991 Supreme Court confirmation hearings, questioning Anita Hill and dismissing sexual harassment allegations as a 'high-tech lynching,' which helped secure Thomas's narrow confirmation.

Joyce directed Bradley Foundation resources to think tanks and advocacy groups that vocally endorsed and defended Clarence Thomas during his 1991 confirmation hearings, countering progressive opposition and helping secure his lifetime appointment, which advanced conservative judicial priorities.

Levin has repeatedly endorsed and defended Justice Thomas's jurisprudence on his programs, highlighting Thomas's originalism in books and commentary, especially during controversies like the 2020 election cases and affirmative action rulings.

Leonard Leo's close personal friendship with Justice Clarence Thomas has been challenged, particularly regarding undisclosed financial arrangements involving Ginni Thomas, the justice's wife. Critics and accusations focus on Leo's role in facilitating or enabling payments to Ginni Thomas, raising questions about whether Justice Thomas properly disclosed related gifts or income, which could violate federal ethics laws and judicial ethics rules. Combined with Leo's influence over judicial nominations, these undisclosed payments and his role in arranging them have created an appearance of impropriety and potential violations.

Leonard Leo played a critical role in the confirmation of Clarence Thomas to the U.S. Supreme Court in 1991, working closely with then-Senator John Danforth and the Bush administration to secure the nomination and confirmation. He has since maintained a close personal friendship with Justice Thomas and has been instrumental in supporting his judicial career. Leo leveraged his network within the Federalist Society and broader conservative legal circles to build political support for Thomas's confirmation and to provide ongoing intellectual and financial backing for Thomas's conservative jurisprudence. Leo also arranged consulting payments to Ginni Thomas, Clarence Thomas's wife, through a group he led, further solidifying their alliance.