Barrett, in one of her first public speeches as a justice, told an audience Sunday in Kentucky that "this court is not comprised of a bunch of partisan hacks," according to the Louisville Courier-Journal.
Breyer, asked about those comments in an interview with the Washington Post on Monday, said that he agrees "with I think the approach is that she's taking there."
"As I’ve said, it takes some years and then you gradually pick up the mores of the institution. And the mores of the institution -- you’re a judge, and you better be there for everybody," said Breyer, the court's oldest member and most senior liberal. "Even if a Democrat or Republican appointed you - you’re there as a judge."
Barrett appeared to echo that sentiment in her speech, telling the audience that differences among "judicial philosophies are not the same as political parties."
Her message may have been undercut, however, by the fact that the event was hosted by Senate Republican Leader Mitch McConnell inside an academic center named in his honor. Several progressive legal groups and independent judicial watchdogs criticized the the optics.
"If Justice Barrett wants the Supreme Court not to be seen as partisan, she should avoid being hosted by a center named after the most partisan person in America," said Gabe Roth, executive director of Fix The Court, a nonpartisan advocacy group. "There’s value in members of the high court speaking to audiences outside of Washington, but that concept is corrupted when stretched to rationalize appearing at events that look and sound like political pep rallies."
Breyer was not asked about and did not comment on the connection with McConnell. His appearance came as part of a media tour for his new book, "The Authority of the Court and the Peril of Politics."
The public defense of the court as a nonpartisan institution comes at a fraught time for the justices and their credibility. The Court's approval rating has dipped below 50% for the first time since 2017 and down 9-points from a decade high just last year, according to Gallup.
This month, the court became embroiled in a dramatic and highly divisive debate over abortion in Texas, after refusing to block an unprecedented law that effectively outlaws the procedure across the state by a narrow 5-4 vote.
Barrett voted with the majority; Breyer dissented.
"The timing wasn’t very good for my book because it’s pretty hard to believe when a case like those come along that we’re less divided than you might think," Breyer lamented.
"A lot of people will strongly disagree with many of the opinions or dissents that you write, but still, internally, you must feel that this is not a political institution, that this is an institution that's there for every American," he said.