TBILISI, Georgia — President Mikheil Saakashvili of Georgia conceded defeat in parliamentary elections on Tuesday and declared himself an opposition politician, an extraordinary event in a country whose other post-Soviet leaders have left office under pressure from chanting crowds and the threat of civil war.
Mr. Saakashvili, 44, saw his presidency as a mission to wrench Georgia free of its Soviet past, which made it especially striking to see him let it go so calmly, a bronze bust of Ronald Reagan visible behind his right shoulder.
A coalition of opposition groups, called Georgian Dream, won the vote on Monday by 55.1 percent to 40.1 percent, the Central Election Commission reported on Wednesday morning, with about 96 percent of precincts reporting.
“You know well that the views of this coalition were, and still are, fundamentally unacceptable for me,” Mr. Saakashvili said. “There are very deep differences between us, and we believe that their views are extremely wrong. But democracy works in this way — the Georgian people make decisions by majority. That’s what we, of course, respect very much.”
Tbilisi, the capital, had become increasingly tense as the elections approached, and many feared that they would end in a confrontation between government forces and the throngs of voters who had coalesced around Mr. Saakashvili’s challenger, the billionaire philanthropist Bidzina Ivanishvili. Both of Mr. Saakashvili’s predecessors, Zviad K. Gamsakhurdia and Eduard A. Shevardnadze, left office in chaotic circumstances, hoping to avoid civil unrest.
Mr. Saakashvili’s concession opens the door to another unknown. He will remain president until next year, so he will have to serve alongside Mr. Ivanishvili, who will most likely be prime minister.
An hour after Mr. Saakashvili’s concession, though, Mr. Ivanishvili excoriated him at length, calling him “the main cause of all the bad things in Georgia,” and said the two men could not collaborate.
Mr. Ivanishvili then said Mr. Saakashvili should resign and schedule new presidential elections. “This will be the end of his problems,” he said at a news conference. “This would be a good way for him to keep his image. This would be good for Georgia.”
Mr. Saakashvili’s national security adviser, Giga Bokeria, went on television to make it clear that there would be no new presidential elections.
“If someone is interested in provoking a crisis, this is a very dangerous choice,” he said. “It is not about personalities. It is about Georgian democracy and the will of the people.”
Dozens of United States and European officials had streamed into Tbilisi to serve as consultants or observers, and on the eve of the vote it was difficult to traverse a hotel lobby without passing an American congressman. Under Mr. Saakashvili, Georgia has been the United States’ staunchest ally in the post-Soviet orbit, and its capital features a statue of Mr. Reagan and a street named after former President George W. Bush. Western officials have frequently warned Mr. Saakashvili about his excesses, including when the police used rubber bullets and water cannons to disperse demonstrators in 2007.
As the election approached, American officials and other interlocutors shuttled between Mr. Ivanishvili and Mr. Saakashvili, hoping to defuse tensions in the event of a disputed vote. Representative David Dreier, Republican of California, said he quoted Winston Churchill’s directive, “In victory, magnanimity.”
“This is clearly the most competitive election in the history of the country,” said Mr. Dreier, who led a delegation from the International Republican Institute, an American democracy-building organization. “Let’s hope that brings about a different outcome than the ones we’ve seen in the past — where, basically, you grind your heel into the opposition.”
Senator Jeanne Shaheen, a New Hampshire Democrat who met with Mr. Saakashvili on Tuesday morning, said he showed “his statesmanship, and his commitment to the democratic process, and to continuing the values that he has put in place.”
“Clearly, it was hard,” she said. “It’s never easy to lose.”
Mr. Saakashvili made it clear in his brief remarks that his mind was on his legacy. He was just 36 when he was swept into office by the Rose Revolution, and his plans were big: disbanding the hated traffic police; instituting a zero-tolerance policy that swelled the prison population fourfold; introducing English, not Russian, as the country’s second language; replacing Soviet concrete-slab construction with jaw-dropping glass buildings; and establishing Georgia as a laboratory for free-market policies.
Many of his pet projects were criticized during the campaign, which tapped into frustration over persistent poverty and unemployment, as well as weariness with a clique that had monopolized politics for eight years. In his remarks, Mr. Saakashvili dwelled on the changes that had taken place in society.
“The achievements of the Rose Revolution in the last eight years are very important not only for Georgian history — it is one of the most important periods of Georgia’s multicentury history — but they have turned Georgia into one of the key countries for the rest of the world,” he said. “Therefore, I am deeply confident that ultimately, regardless of what threats these achievements may face within the nearest months or years, their eradication is impossible.”
His decision to step aside clearly resonated deeply with some Georgians.
“We have no tradition of democracy with no shooting,” said Mikheil Sologashvili, 51. “What we’ve had here is, ‘You kicked me out, and I ran away.’ I am so happy that I woke up after the election, and that on the second day, I heard the president say that even though he disagrees, this is the demand of democracy. For me, that is better than if someone gave me the latest model of Mercedes.”
He said it would be a great mistake for Mr. Saakashvili to leave office before his term ends next year. “A big ship leaves big waves behind it,” he said. “He should not leave quickly. He should calm the waters.”
Much attention swung immediately to Mr. Ivanishvili, who is still a mysterious figure to many in the West. A central question is how close Mr. Ivanishvili will bring Georgia to Russia, the country where he earned his billions. Mr. Ivanishvili has promised to use diplomacy to “normalize” the country’s relationship with Russia, which in 2006 closed its markets to imports of wine, fruit and bottled water, stripping many people of their livelihood.
At his news conference on Tuesday, Mr. Ivanishvili said without hesitating that he planned to bring Georgia even closer to the United States and that he, like Mr. Saakashvili, hoped to steer the country toward NATO membership.
However, he went on to inveigh against Mr. Saakashvili, deriding his trademark reforms, as well as recent projects like a plan to build a city, Lazika, on the Black Sea, and a joint construction venture with Donald J. Trump.
Ms. Shaheen, the New Hampshire senator, said she had heard little specific from Mr. Ivanishvili about how he intended to collaborate with Mr. Saakashvili. “Georgian Dream and the opposition said they would never hold elections,” she said of the current government. “They said the elections would never be open and free and fair, that the people of Georgia would not be free to express their will, and, if they did, President Saakashvili would not concede and step down.
“I would point out that they were wrong on all three counts,” she said.