A judge in Missouri ruled Wednesday that the state’s newly drawn congressional map could be used in the November elections, handing Republicans a win in a monthslong battle over redistricting.

Judge Daniel Green of the Circuit Court of Cole County, which includes the state’s capital, Jefferson City, shot down an attempt to subject the new map, which favors Republicans, to a statewide vote in November.

The judge sided with Denny Hoskins, the secretary of state, who had argued that Missouri’s Constitution does not allow a referendum on congressional redistricting and that altering districts now could disrupt midterm elections.

“Changing the maps at this late juncture is not just ‘impractical,’ it is impossible,” Judge Green said in the ruling.

The decision has been appealed to the state’s Supreme Court, according to Charles Hatfield, a lawyer for People Not Politicians, the group that filed the lawsuit and the proposed referendum on the new map.

“There are some more games left to play here,” Mr. Hatfield said. “We are optimistic about our chances at the Supreme Court.”

The decision is a victory for Republicans hoping to maintain narrow control of the U.S. House in the midterm elections. Missouri was one of the first states to try to redraw its maps as part of President Trump’s national push to increase Republicans’ chances of keeping the chamber in the midterms.

The fate of Missouri’s map, which was designed to flip a seat currently held by a Democrat, has been uncertain for months.

Shortly after lawmakers approved the map last year, People Not Politicians began gathering signatures to put the redrawn districts on voters’ ballots in November. In Missouri, if a petition gets enough signatures to challenge a piece of legislation, that legislation is paused until a statewide vote is held.

The petition got enough signatures, according to supporters, but on Aug. 4, Mr. Hoskins, a Republican, said the proposed referendum did not qualify for the ballot. The decision came on the same day as primaries in the state, during which the new map was in use.

Richard von Glahn, executive director of People Not Politicians, said that the ruling was in fact no defeat for those who want to preserve the Democratic seat.

“The most important thing that happened today is that there was a ruling,” he said, adding that “the state has tried to slow down the judicial process for months and now that we are out of Cole County, the real decision will be made. Our case now moves forward.”

Mr. Hoskins could not immediately be reached for comment on Wednesday.

The case now heads to the state’s Supreme Court, which has already ruled in favor of the redistricting effort. In March, it upheld state lawmakers’ ability to redraw the map outside of the typical, once-a-decade cycle.

In Missouri, the deadline to add a referendum to general election ballots is Sept. 8. It was not immediately clear whether the state’s Supreme Court would hear the appeal before then.