Voters at Charleston, South Carolina, have elected the first Republican mayor since 1877 after years of demographic change that has seen large numbers of Black residents leave the city and large numbers of white residents move in.

Mayor-elect William Cogswell defeated the incumbent mayor, John Tecklenburg, 51 percent to 49 percent, in a race decided by 569 votes.

“I think it’s time for a change,” Mr. Cogswell said in an election night speech. “I think people want to see less of the status quo and are looking for a new breath of life into the city.”

Mr. Tecklenburg conceded the race at his watch party on Tuesday night, saying, “I’m as optimistic about the city as I’ve ever been.”

“I’d like to congratulate William Cogswell, and I’d like to ask each and every one of you to give him your support because when Mayor Cogsell succeeds, all of Charleston succeeds,” Mr. Tecklenburg said.

The primary election had attracted the attention of some out-of-state Democrats, with both Governor Newsom and Governor Prizker donating $1,000 to Mr. Tecklenburg’s one-time opponent, Clay Middleton.

Mr. Middleton placed third in the city’s initial election in early November, endorsing Mr. Tecklenburg in the runoff election, which happened on November 21.

Mr. Cogswell is the first Republican mayor to be elected at Charleston since 1877, a sign of ongoing demographic changes that have been reshaping the city’s politics for decades.

Census data collected at Charleson between 1960 and 2020 show a city that has transformed to about two-thirds white from approximately two-thirds Black.

Between 2010 and 2020, the city’s Black population dropped by about 5,000 while the white population grew by about 26,000, and the city’s Hispanic and multi-racial population grew by about 3,400 and 3,600, respectively.

Over the past 60 years, the borders of the city proper have also expanded to include towns and suburbs like Cainhoy and Daniel Island, which has led to changes in who is voting in city elections.

Black voters in South Carolina have taken on an increased importance in internal Democratic politics in recent years, being seen as catapulting President Biden to the nomination in 2020.

The Democratic Party then moved South Carolina to the front of its party nominating calendar, saying the electorates in Iowa and New Hampshire are not as representative of the Democratic coalition as the electorate in South Carolina. Critics have argued that the move was a reward for the state, which helped lock up the nomination for Mr. Biden.