Portugal’s Socialist Party conceded defeat on Sunday night in a very tight national election that ended the party’s eight years in power and reflected the country’s drift to the right, which follows a broader trend in Europe.

That shift was marked by the ascent of Chega, an anti-establishment, right-wing party, which skyrocketed from recent irrelevance to become the third most popular party in Portugal.

The Socialist Party, which has been hobbled by a corruption investigation, had been running neck and neck with the Democratic Alliance, a center-right coalition, until late in the evening, when the Socialist leader conceded at a news conference.

The Socialists and the Democratic Alliance had each garnered about 29 percent of the vote, with about 99 percent of the voting districts having counted their ballots. Ballots cast abroad, which elect four parliamentary seats, had yet to be counted, but the Socialist Party leader, Pedro Nuno Santos, said that those ballots were unlikely to make up for the votes they needed to win.

“Everything indicates that the Socialist Party did not win the election,” Mr. Nuno Santos said at the news conference.

His concession paved the way for Luís Montenegro, the leader of the Social Democratic Party, the major party within the Democratic Alliance, to form a government. “It seems undeniable that the Democratic Alliance won the elections and that the Socialists lost,” Mr. Montenegro said at a news conference.