Roberts was originally nominated by President George W. Bush as an associate justice to succeed Sandra Day O'Connor, who had announced her retirement, effective with the confirmation of her successor.

On October 3, Roberts took the judicial oath provided for by the Judiciary Act of 1789, prior to the first oral arguments of the 2005 term.

The Roberts Court commenced with Roberts as Chief Justice and the remaining eight associate justices from the Rehnquist Court: Stevens, O'Connor, Antonin Scalia, Anthony Kennedy, David Souter, Clarence Thomas, Ruth Bader Ginsburg, and Stephen Breyer.

[3] In 2022, Breyer announced his retirement effective at the end of the Supreme Court term, assuming his successor was confirmed, in a letter to President Joe Biden.

[11][16] Though the Court sometimes does divide along partisan lines, attorney and SCOTUSblog founder Tom Goldstein has noted that more cases are decided 9–0 and that the individual justices hold a wide array of views.

[20] Some commentators have also noted that Roberts uses his vote in high-profile cases to achieve a facially-neutral result that sets up for larger conservative rulings in the future.

"[22] Regarding Roberts' contemporaneous peers on the bench, his judicial philosophy is seen as more moderate and conciliatory than that of Antonin Scalia and Clarence Thomas.

[18][20] Roberts has not indicated any particularly enhanced reading of originalism or framer's intentions as has been plainly evident in Scalia's speeches and writings.

That opinion drew ire from critics who argued that Roberts and the conservative bloc manufactured a doctrine to thwart climate reforms.

[40] Aaron Regunberg in The New Republic criticized the Supreme Court for playing Calvinball, a game with no rules except for those made up as they go.

[41] In a July 2022 research paper entitled "The Supreme Court's Role in the Degradation of U.S. Democracy," the Campaign Legal Center, founded by Republican Trevor Potter, asserted that the Roberts Court "has turned on our democracy" and was on an "anti-democratic crusade" that had "accelerated and become increasingly extreme with the arrival" of Trump's three appointees.