Breyer, a nominee of President Bill Clinton, has served his entire tenure on a court with conservatives in the majority that became more conservative the longer he served. He is retiring at a time when six of the nine justices are ideologically to his right and chosen by Republican presidents.

But Breyer looked for compromise even as he defended affirmative action in university admissions, same-sex marriage and the First Amendment.

“While he was frequently in dissent over the course of his time on the Court, he always remained optimistic, confident that in the end our government will work, and the courts will play an important role in making that happen. That optimism and confidence will also be an important part of his legacy.”

Last term, Chief Justice John G. Roberts Jr. assigned Breyer some of the court’s most significant cases. He wrote the majority opinion when the court turned down a Republican-led challenge to the Affordable Care Act. And in an 8-to-1 ruling, he defended the First Amendment rights of public school students in a case involving the punishment of a high school cheerleader for a profane post on social media.

“It might be tempting to dismiss B.L.’s words as unworthy of the robust First Amendment protections discussed herein. But sometimes it is necessary to protect the superfluous in order to preserve the necessary,” he wrote, using the initials of the cheerleader.

In recent emergency rulings on the death penalty, abortion and pandemic restrictions, Breyer has dissented along with liberal Justices Sonia Sotomayor and Elena Kagan. When the court ended an eviction moratorium put in place by the Centers for Disease Control and Prevention, Breyer said the majority was abandoning its usual procedures.

“These questions call for considered decisionmaking, informed by full briefing and argument. Their answers impact the health of millions,” Breyer wrote.

On the bench, Breyer routinely speaks more during oral argument than any other justice. Harvard Law professor Richard Lazarus, who closely studies the justices, compared Breyer’s lengthy statements and hypotheticals to a professor teaching a large class who then stops abruptly and asks something like, “Well, what do you think?”

Lazarus said Breyer should not be classified simply as a “liberal,” but is much better understood as the court’s resident intellectual — more “law professor than lawyer and more pragmatist than activist.”

“He is the first of his colleagues to eschew overarching jurisprudential philosophies in favor of practical, commonsense solutions consonant with basic notions of social justice,” he wrote in a column about Breyer shared with The Washington Post.

But Lazarus cautioned not to mistake Breyer’s pragmatism for a lack of passion.

“His decades of service on the Court make clear his deep commitment to social justice and the fundamental role of the judiciary in its pursuit,” Lazarus wrote.

In 2000, Breyer wrote for the majority in striking down a Nebraska law banning late-term abortions because it did not include an exception for the health of pregnant women. He lobbied his close friend on the court, Justice Sandra Day O’Connor, to provide the fifth vote, according to an account by Jeffrey Toobin in his book about the court, “The Nine.” Breyer also acknowledged in his opinion the deep divisions over the issue.

“Millions of Americans believe that life begins at conception and consequently that an abortion is akin to causing the death of an innocent child,” Breyer wrote. “Other millions fear that a law that forbids abortion would condemn many American women to lives that lack dignity, depriving them of equal liberty and leading those with least resources to undergo illegal abortions with the attendant risks of death and suffering.”

He subsequently wrote the court’s decisions to strike down restrictions in Texas and Louisiana that required doctors who perform abortions to have admitting privileges at nearby hospitals.

In 2005, Breyer cast the deciding votes in two cases involving public displays of the Ten Commandments that showed his interest in outcomes that avoided conflict. The court allowed a long-standing six-foot-tall monument on the Texas Capitol grounds but rejected newer displays installed in Kentucky courthouses.

After 20 years on the court, Breyer, joined by Ginsburg, used a 2015 dissent in a lethal injection case to say that he had doubts about whether the death penalty can be constitutionally applied and to call for the court to reexamine the issue. Breyer wrote that the country’s use of the death penalty has dramatically changed since the court upheld capital punishment in 1976.

“The imposition and implementation of the death penalty seems capricious, random, indeed, arbitrary,” he wrote. “From a defendant’s perspective, to receive that sentence, and certainly to find it implemented, is the equivalent of being struck by lightning.”

Neal Katyal, who was law clerk for Breyer and a former acting U.S. solicitor general, described the justice on Wednesday as a “listener instead of a pontificator.”

While Breyer’s opinions will have a “deep impact on our democracy for decades to come,” Katyal wrote in a Washington Post opinion piece, it is his “execution of those rulings, and the way he carried himself on the court” that may prove a greater legacy.

Robert Barnes contributed to this report.