The presidential candidate of the center-left coalition that has governed Uruguay for 15 years conceded defeat on Thursday, four days after a close and contentious runoff election, as the nation joined others in the region in shifting rightward.

The concession ushers in Luis Lacalle Pou of the center-right National Party as the country’s new leader. It also spells an end to the tenure of the Broad Front, a coalition of leftist and center-left parties that oversaw the legalization of abortion, same-sex marriage and the sale of marijuana.

Mr. Lacalle Pou’s rival, Daniel Martínez of the Broad Front, conceded even as the vote count continued on Thursday. Mr. Martínez acknowledged on Twitter that the counting of provisional ballots would “not modify the trend” and said he would meet with Mr. Lacalle Pou on Friday.

Brazil, Chile, Bolivia and Colombia have also moved rightward to varying degrees, though Argentina recently elected a center-left president. Venezuela’s leftist government is hanging on despite political and economic turmoil.