From her first week on the Supreme Court bench in October to the final day of the term that ended last week, Justice Ketanji Brown Jackson did something remarkable for a junior justice: She established herself as a distinctive voice on the court.

“She was not cowed by her surroundings or the historical import of her appointment,” said Melissa Murray, a law professor at New York University. “She came to play.”

Other justices have spoken about taking years to find their footing at the court, but Justice Jackson, the first Black woman to serve on the Supreme Court, wasted no time.

Chief Justice John G. Roberts Jr. did not write his first solo dissent in an argued case until 16 years into his tenure. Justice Jackson issued three such dissents in her first term.

“Justice Jackson really hit the ground running,” said Pamela S. Karlan, a law professor at Stanford. “And the lines are pretty sharply drawn between her and the majority on criminal justice issues as well as racial justice issues.”

On her second day of arguments, she set out a sort of mission statement, asking a long series of questions about the history of the 14th Amendment, adopted after the Civil War and meant to protect formerly enslaved Black people. “That’s not a race-neutral or race-blind idea,” she said.

In focusing on the original meaning of the amendment, she adapted a conservative method to press for a liberal result. When the court issued its 5-to-4 decision in the case, on voting rights in Alabama, she was on the winning side.

During her confirmation hearings, to the surprise of some, Justice Jackson declared herself an originalist, meaning, she explained, that she interprets the Constitution based on how it was understood at the time it was adopted. “I look at the text to determine what it meant to those who drafted it,” she said.

But Justice Jackson’s originalism has an unmistakably progressive orientation, one that takes account of not only the original Constitution but also the three transformative amendments adopted in the wake of the Civil War.

“In her first term on the bench, Justice Jackson challenged the dominant conservative narrative of the Constitution, marshaling constitutional history to make clear that our national charter demands meaningful equality and supports a genuinely thriving multiracial democracy,” said Elizabeth Wydra, president of the Constitutional Accountability Center, a liberal group. “This could mark a new chapter for the court, where we see a real, sustained challenge to the conservative originalism of the current supermajority, equally rooted in text and history.”

On the last day of the term, after two days in which she and her two liberal colleagues suffered stinging losses in 6-to-3 decisions on affirmative action, student debt and a clash between free speech and gay rights, Justice Jackson issued one last dissent before the court’s summer break. The court should have agreed to hear a challenge to an 1890 felon-disenfranchisement law in Mississippi that was the product of avowed racism, she wrote.

“Constitutional wrongs do not right themselves,” she wrote.

The day before, she had been the subject of a long and harsh passage spanning more than six pages in a concurring opinion from Justice Clarence Thomas, the only other Black member of the court, in the case that rejected race-conscious admissions programs at Harvard and the University of North Carolina.

“As she sees things, we are all inexorably trapped in a fundamentally racist society, with the original sin of slavery and the historical subjugation of Black Americans still determining our lives today,” Justice Thomas wrote, adding that “on her view, almost all of life’s outcomes may be unhesitatingly ascribed to race.”

In a footnote in her dissenting opinion, Justice Jackson dismissed the critique. “Justice Thomas’s prolonged attack responds to a dissent I did not write,” she said, adding that his opinion “also demonstrates an obsession with race consciousness that far outstrips my or U.N.C.’s holistic understanding that race can be a factor that affects applicants’ unique life experiences.”

Justice Thomas’s opinion was striking, Professor Murray said. “Parts of his concurrence read as a Black elder chiding and chastising an errant Young Turk who has publicly contradicted him and failed to show him sufficient deference,” she said. “It’s almost as if he expects racial solidarity from her and is put out when it’s not forthcoming in the manner he expected.”

The principal dissent in the case, from Justice Sonia Sotomayor, was just as vigorous as the one from Justice Jackson. “But Thomas’s fire is not aimed at Sotomayor,” Professor Murray said. “It’s reserved for Jackson.”

Justice Jackson is a member of a three-justice liberal minority, which means she typically does not have much power to affect the outcomes of major cases. But sometimes she may be able to make important contributions at the margins.

When the challenge to the race-conscious admissions program at U.N.C. was argued in October, Justice Jackson asked a telling question about hypothetical application essays — one from a white fifth-generation legacy and the other from a Black student whose ancestors had been enslaved.

“The first applicant would be able to have his family background considered and valued by the institution as part of its consideration of whether or not to admit him,” she said, characterizing an aspect of the challengers’ argument, “while the second one wouldn’t be able to because his story is in many ways bound up with his race and with the race of his ancestors.”

When the decision in the case was issued eight months later, Justice Jackson was on the losing side. But Chief Justice Roberts’s majority opinion contained a caveat: “Nothing in this opinion should be construed as prohibiting universities from considering an applicant’s discussion of how race affected his or her life, be it through discrimination, inspiration or otherwise.”

Professor Murray said that was a grudging response to Justice Jackson. “I don’t think John Roberts would have included that paragraph were it not for her incisive hypothetical,” she said.

In all, said Roman Martinez, a Supreme Court specialist at Latham & Watkins, “Justice Jackson had an impressive year on the court.”

“She was a forceful and enthusiastic questioner at oral argument, wrote sharp opinions and developed an intriguing cross-ideological alliance with Justice Gorsuch supporting fairness and due process for the ‘little guy’ in disputes against government authority,” Mr. Martinez said.

In May, for instance, the court unanimously ruled that states that seize and sell private property to recoup unpaid taxes violate the Constitution’s takings clause if they retain more than what the taxpayer owed. Justice Neil M. Gorsuch issued a concurring opinion that explored another possible constitutional violation: the Eighth Amendment’s prohibition of “excessive fines.”

The opinion was joined by only one other member of the court: Justice Jackson. That was also true of a concurring opinion by Justice Gorsuch in a copyright dispute involving Andy Warhol, and of a dissent by Justice Gorsuch from an order temporarily keeping a pandemic-era immigration measure in place.

Justice Jackson is 52, and she will probably serve for several decades. The composition and direction of the court will doubtless change. For now and for the most part, Professor Murray said, “she’s writing for the public and for a future where she may not always be in the dissent.”