Then, less than an hour later, he got down to the business of the Supreme Court, as the justices heard arguments in a labor-management dispute.
Judges in Maine and Washington state took different sides on what federal laws require. The Supreme Court took up the cases to resolve the matter.
Roberts, attentive and businesslike, asked brief questions during the hourlong arguments to clarify points raised by the lawyers. As is often the case, it was not apparent how the justices likely would rule, and the answer might not come for a few months.
The first case of the Roberts Court made for a decided contrast with the ceremony that preceded it - and the weeks leading up to the confirmation of the new chief justice.
Thursday, just after the Senate confirmed his nomination, Roberts took an oath of office at the White House so he could start work. His formal investiture as the 109th justice of the Supreme Court came at 9:15 a.m. yesterday.
With the president in attendance, the clerk of the court read a formal proclamation in which Bush appointed Roberts, with the consent of the Senate, to be the chief justice of the United States.
At 50, Roberts is the youngest person to hold that post since John Marshall, then 45, was sworn in 1801. As the ceremony began, Roberts sat in a chair that belonged to Marshall. After the proclamation was read, he was called to the bench while the other eight justices stood.
After Roberts swore to "administer justice without respect to persons," the senior member of the court at 85, Justice John Paul Stevens, wished him "a long and happy career in our common calling."
Also yesterday, the Supreme Court was asked to intervene in a Patriot Act case in which plaintiffs claim authorities used the anti-terrorism law to cloak library records demands from the FBI.
The American Civil Liberties Union filed the emergency appeal, on behalf of an anonymous client, but the paperwork is censored and gives few details.
The ACLU has argued that a gag order prevents its client, apparently librarians in Connecticut, from participating in a debate over whether Congress should reauthorize the Patriot Act.
A federal judge said the gag order had "the practical effect of silencing individuals with a constitutionally protected interest in speech and whose voices are particularly important in an ongoing national debate about the intrusion of governmental authority into individual lives."
The 2nd U.S. Circuit Court of Appeals in New York put the decision on hold, and the Supreme Court was asked to overrule the appeals court.
Federal prosecutors have maintained that secrecy about records demands is necessary to keep from alerting suspects and jeopardizing terrorism investigations. They contend the gag order prevents only the release of the client's identity.
The Patriot Act, passed shortly after the 2001 terror attacks, allowed expanded surveillance of terror suspects, increased use of material witness warrants to hold suspects incommunicado and secret proceedings in immigration cases. Some key provisions expire at the end of the year.
Yesterday, a smiling Justice Sandra Day O'Connor was in her seat despite having announced her retirement in July.
Her presence might be mostly symbolic, however. That is because the justices' votes count only when a decision is handed down, and it usually takes several months for the court to decide an important case.
If White House counsel and Supreme Court nominee Harriet E. Miers wins Senate confirmation by December, O'Connor would be gone before the court handed down its first significant rulings.
One high-profile case was heard yesterday. Lawyers for the Bush administration are challenging Oregon's Death with Dignity Act, a voter-approved measure that permits dying people to obtain lethal medication from a doctor.
If O'Connor's retirement occurs before the court decision becomes official, and the remaining eight justices who heard oral arguments in the case split 4-4, then the justices probably would have the case reargued before the new nine-member court.
David G. Savage writes for the Los Angeles Times. The Associated Press contributed to this article.