WASHINGTON — The Kansas Supreme Court on Wednesday allowed the state to adopt a new congressional map that a lower court had ruled unconstitutional, handing a victory to Republicans and very likely costing the state’s Democrats their only seat in Congress.

The map, enacted by the Republican-controlled State Legislature over a veto by the governor, splits metropolitan Kansas City along both racial and partisan lines, the lower court had ruled last month, in an effort to break Democrats’ hold on the Third Congressional District. It is the only one of the state’s four House seats held by a Democrat.

The Supreme Court’s two-page ruling overturning the lower court decision explained neither the reasoning behind the verdict nor how the seven justices had voted. It said a full opinion would be issued later, but the ruling means that the Republican map boundaries will be used in elections in November. The filing deadline for candidates is June 10.

The decision would appear to run counter to a trend in other state courts, in both Democratic and Republican states, to aggressively strike down gerrymandered political maps drawn to ensure electoral gains or protect congressional seats for one party.

Lawyers for the Campaign Legal Center and the American Civil Liberties Union had argued that the Republican map in Kansas violated the State Constitution’s guarantees of the right to vote, of equal protection and of free speech and assembly.

High courts cited similar clauses in other state constitutions this spring when striking down partisan gerrymanders in North Carolina, Maryland and New York, as did the Supreme Court of Pennsylvania in 2018, when it issued the first state court ruling against a gerrymander on grounds that it was overly partisan.

The lower court ruling in the Kansas case, by a state district court judge in Kansas City, had embraced the same arguments.

“The Kansas Constitution provides strong protections for political equality and against partisan gerrymandering,” Judge Bill Klapper wrote. He added, “It recognizes that ‘all political power is inherent in the people’ and that ‘all free governments are founded on their authority, and are instituted for their equal protection.’”

“Decisions from sister states buttress this conclusion,” he wrote, noting that the North Carolina Constitution contains similar clauses.

Judge Klapper’s decision, which was made obsolete by the Supreme Court’s ruling on Wednesday, barred the Legislature from holding elections under the plan and requested that lawmakers draw new maps “as expeditiously as possible.”

Gov. Laura Kelly, a Democrat, had vetoed the congressional map after Republican supermajorities in the State House and State Senate approved it in late January, but the Legislature overrode her veto.

Republican legislators had argued that the Third District remained winnable by a Democratic candidate, and that the new boundaries were a reasonable way to account for population changes and ensure that all four districts contained the same number of residents.

In a hearing on the case before the Supreme Court on Monday, the state solicitor general, Brant M. Laue, a Republican appointee, argued that the Kansas Constitution recognized only two discrimination-based challenges to political maps: racial bias, and the concept of one person, one vote.

Allowing a third challenge, rooted in discrimination against members of a political party, he said, would take the court into uncharted territory.

“Where does it stop?” he said. “Will it be age? Will it be gerrymandering based on religion?” Asked whether he could envision any instance in which a partisan gerrymander could be ruled unconstitutional, Mr. Laue replied, “I don’t believe so, under the Kansas Constitution.”

He noted that the U.S. Supreme Court reached the same conclusion in 2019 when it ruled that partisan gerrymanders were a political issue, beyond the court’s jurisdiction.

The senior vice president of the Campaign Legal Center, Paul M. Smith, said the ruling was “a slap in the face to voters and runs afoul of the democratic values spelled out in Kansas’s own Constitution.”

The ruling appeared to be a setback for the growing movement to challenge partisan maps in state courts, an avenue the U.S. Supreme Court left open in its 2019 opinion.

Josh Douglas, an expert on state election law at the University of Kentucky College of Law, said the release of the justices’ written opinion could further clarify the impact of the decision. A sweeping declaration along the lines of Mr. Laue’s argument — that the court had no authority over gerrymanders, or that the rights in the State Constitution did not apply to partisan maps — could resonate in future state court cases, he said.

“If it lays down a marker,” he said, “it’s concerning” for opponents of partisan gerrymanders.