Justice Stephen Breyer to officially retire Thursday at noon, swear in Ketanji Brown Jackson

Supreme Court Justice Stephen Breyer, the most senior member of the U.S. Supreme Court's liberal wing, said he will officially step down from the bench at noon on Thursday, and the court announced he will then swear in his former law clerk -- Ketanji Brown Jackson -- to take his place on the bench, becoming the nation's first Black female justice.

"It has been my great honor to participate as a judge in the effort to maintain our Constitution and the Rule of Law," Breyer wrote in a letter to President Joe Biden dated Wednesday.

Breyer's retirement fulfills the wish of Democrats who lobbied for his exit to make way for Biden's first nominee to the court.

Jackson will take both her oaths at noon -- Chief Justice John Roberts administering the constitutional oath and Justice Breyer delivering the judicial oath. Her presence will mark the first time four women will be on the Supreme Court at the same time.

Progressive activists had imposed unprecedented public pressure on Breyer, who was nominated in 1994 by President Bill Clinton, to retire. Breyer was first appointed to the federal bench in 1980 by President Jimmy Carter, going on to serve 13 years as an appellate judge until Clinton elevated him to replace Justice Harry Blackmun on the Supreme Court in 1994. The Senate confirmed him 87-9.

Last term, Breyer authored major opinions upholding the Affordable Care Act, affirming free speech rights of students off-campus and resolving a multi-billion dollar copyright dispute between two titans of American technology, Google and Oracle.

His retirement relatively early in the Biden presidency, while Democrats retain a razor-thin majority in the U.S. Senate, helped to ensure his seat would be filled with someone who shares his judicial philosophy.

Breyer has described differences among the justices as contrasts in "philosophical outlook" rather than differences of politics and chaffed at the labeling of justices as "liberal" or "conservative."

"Politics to me is who's got the votes. Are you Republican or Democrat? I don't find any of that here," he told ABC News Chief Washington Correspondent Jonathan Karl in 2015.

While he never enjoyed the rock-star status held by Ginsburg, Breyer has long been revered and celebrated as a consensus-seeker and happy warrior throughout his 27 years on the court. He has also been one of the few justices to be a regular attendee at State of the Union addresses before a joint session of Congress.

Asked in 2017 how he would like to be remembered, Breyer told an interviewer: "You play the hand you're dealt. You're dealt one. And you do the best with what you have. If people say yes, he did, he tried, he did his best and was a decent person, good."

Ketanji Brown Jackson to fill Breyer's seat

Jackson, 51, who currently sits on the U.S. Court of Appeals for the D.C. Circuit, will fill Justice Breyer's seat, and become the first Black woman to sit on the nation's highest court. With Jackson's ascension to the bench, for the first time, white men will not represent the majority of justices on the Supreme Court.

President Joe Biden formally announced Jackson's nomination earlier this year and fulfilled a campaign promise made ahead of the South Carolina primary when he relied heavily on support from the state's Black voters and Rep. Jim Clyburn.

"For too long our government, our courts haven't looked like America," Biden said in February from the White House. "And I believe it is time that we have a court that reflects the full talents and greatness of our nation with a nominee of extraordinary qualifications."

Jackson, who will also be the nation's first former public defender to sit on the high court, served as a clerk for Breyer from 1999 to 2000 and called it "extremely humbling to be considered" for his seat.

"I know that I could never fill his shoes, but if confirmed, I would hope to carry on his spirit," she said.

Three Republicans -- Sens. Susan Collins, Lisa Murkowski and Mitt Romney -- joined Senate Democrats in voting to confirm Jackson in April, marking a solid, bipartisan win for the Biden White House.