The Supreme Court on Thursday reversed a lower court’s ruling that a congressional voting map in South Carolina was an unconstitutional racial gerrymander that resulted in the “bleaching of African American voters” from a district.

The vote was 6 to 3, with the court’s three liberal members in dissent.

A unanimous three-judge panel of the Federal District Court in Columbia, S.C., ruled in early 2023 that the state’s First Congressional District, drawn after the 2020 census, violated the Constitution by making race the predominant factor.

The panel put its decision on hold while Republican lawmakers appealed to the Supreme Court, and the parties asked the justices to render a decision by Jan. 1. After that deadline passed, the panel said in March that the 2024 election would have to take place under the map it had rejected as unconstitutional.

“With the primary election procedures rapidly approaching, the appeal before the Supreme Court still pending and no remedial plan in place,” the panel wrote, “the ideal must bend to the practical.”

In effect, the Supreme Court’s inaction had decided the case for the current election cycle.

The contested district, anchored in Charleston, had elected a Republican every year since 1980, with the exception of 2018. But the 2020 race was close, with less than one percentage point separating the candidates, and Republican lawmakers “sought to create a stronger Republican tilt” in the district after the 2020 census, the panel wrote.

The lawmakers achieved that goal, the panel found, in part by the “bleaching of African American voters out of the Charleston County portion of Congressional District No. 1.”

The new House map moved 62 percent of Black voters in Charleston County from the First District to the Sixth District, a seat that Representative James E. Clyburn, a Black Democrat, has held for 31 years.

The move helped make the new First District a Republican stronghold. In November, Nancy Mace, the Republican incumbent, won re-election by 14 percentage points.

Republican lawmakers acknowledged that they had redrawn the First District for partisan gain. But they said they had not considered race in the process.

The panel ruled that the district’s boundaries violated the Constitution. But the panel rejected challenges to two other House voting districts, saying that civil rights groups had failed to demonstrate that the districts had been predominantly drawn to dilute Black voting power.

The Supreme Court has called for very close scrutiny of a state’s actions when race is shown to be the predominant reason for drawing legislative districts. That principle, rooted in the Constitution’s equal protection clause, is often invoked to limit the creation of districts that empower minority voters.

In this case, though, the challenge came from the opposite direction, with civil rights groups saying that the map hurt Black voters by moving them from one congressional district to another.

In their Supreme Court appeal, South Carolina Republicans argued that the panel should have presumed that they had acted in good faith, as required by Supreme Court precedent, and analyzed the district as a whole.

“The result,” the lawmakers wrote, quoting from an earlier decision, “is a thinly reasoned order that presumes bad faith, erroneously equates the purported racial effect of a single line in Charleston County with racial predominance across District 1, and is riddled with ‘legal mistakes’ that improperly relieved plaintiffs of their ‘demanding’ burden to prove that race was the ‘predominant consideration.’”

The challengers, represented by the American Civil Liberties Union and the N.A.A.C.P. Legal Defense and Educational Fund, told the justices that “the panel correctly found that race was the gerrymander’s primary vehicle.”

“That predominant reliance on race is impermissible even if mapmakers used race as a proxy for politics,” the challengers’ brief said.

The case, Alexander v. South Carolina State Conference of the N.A.A.C.P., No. 22-807, is superficially similar to one from Alabama in which the court ruled in June that state lawmakers had diluted the power of Black voters in drawing a congressional voting map. But the two cases involve distinct legal principles.

The Alabama case was governed by the Voting Rights Act, the landmark civil rights statute, and the one from South Carolina by the Constitution’s equal protection clause. The two can tug in different directions.