The mayor of Romania’s capital of Bucharest won the country’s presidential election, placing a staunch pro-European politician in power and capping months of political instability.

Nicusor Dan , a centrist, claimed victory in Sunday’s election over a far-right candidate, George Simion , who had praised President Trump and promised to “Make Romania Great Again.” With nearly all of the ballots counted, preliminary results showed Dan had gotten about 54% of the vote, while Simion trailed with nearly 46%.

Romania, which hosts two North Atlantic Treaty Organization bases and a major air-defense system, has been rocked by political uncertainty since last year. The country’s Constitutional Court canceled a presidential election in December over allegations that a Russian social-media influence operation had skewed election results to favor a little known right-wing candidate, Calin Georgescu.

Georgescu was banned from running again in the redo election. Simion, a telegenic politician from Romania’s far right who promised to make Georgescu prime minister, led in the first round of voting earlier this month

In contrast to Romania’s other flashier politicians, Dan, who studied mathematics, has a short cropped mop of curly hair and is known to speak about policy while staring at the floor. He has advocated for stronger European ties and more aid to Ukraine, while fighting corruption at home.

“I cast my vote for maintaining Romania’s European direction and for solid cooperation with our European partners, rather than a path which leads to Romania’s isolation,” said Dan, 55 years old, voting in his hometown of Fagaras, in central Romania. He later traveed to Bucharest, where he has served as mayor for four years.

“Today marks a turning point,” he added.

Presidential candidate Nicusor Dan speaks, as he reacts to exit polls of Romania’s second round of the presidential election, in Bucharest, Romania, May 18, 2025. REUTERS/Stoyan Nenov

An independent candidate, he broke from Romanian party politics and its fractious landscape in 2017. His outsider image likely appealed to many voters who sought a break from the current government, which critics say has increasingly tried to influence business and the justice system.

Dan has said he plans to fight organized crime and corruption, empowering some of the state anticorruption agencies that analysts said had been defanged in recent years. He also said he plans to boost Romania’s military spending, which is just above 2% of gross domestic product, to 3.5% in the next five years.

Simion rankled NATO allies by advocating for neutrality between Russia and Ukraine and was seen by some as too sympathetic to Russia. Simion had been banned from both Moldova and Ukraine. No explanation was ever given for the ban, but a former Moldovan defense minister said it was because of alleged links with Russian intelligence agencies.

On Sunday, Simion leveled accusations of voter fraud, without providing evidence. He also declared victory despite the exit polls.

Pavel Durov , the Russian-born founder of social-media messaging app Telegram, said he had refused to comply with a request from a Western government “to silence conservative voices in Romania ahead of today’s presidential elections.” Durov didn’t offer further detail or name the government.

Dan’s campaign said the statement by Durov, made on Sunday, was itself a form of interference in the election.

Romania captured the attention of the U.S. earlier this year when the annulment of the previous election sparked criticism by Vice President JD Vance . Simion has tried to further strengthen ties with Republicans in the U.S. He spent a week in the U.S. at the height of the campaign, giving interviews to antiestablishment right-wing commentators such as Steve Bannon and Jack Posobiec .

A supporter of Presidential candidate Nicusor Dan holds up a Romanian flag, as she reacts following exit polls in Romania’s second round of the presidential election, in Bucharest, Romania, May 18, 2025. REUTERS/Andreea Campeanu TPX IMAGES OF THE DAY

In the lead-up to the election, Simion voiced public support to Polish right-wing presidential candidate, Karol Nawrocki , who was running for the country’s former ruling Law and Justice Party, which was voted out of office in 2023. Simion had said in an interview with a conservative U.S. magazine that he and Nawrocki could form a pro-Trump alliance in Europe.

On Sunday, Nawrocki came in a close second in the first round of voting behind Rafal Trzaskowski from the current center-left ruling coalition, exit polls showed. The two beat out Slawomir Mentzen , of the Kofederacja Party, which has styled itself as a bastion of antiestablishment sentiment. Konfederacja has advocated for the end of support for Ukraine and has played up Poles’ growing weariness of the war and support for Ukrainian refugees in the country.

The victory of Dan in Romania will likely help boost economic stability in the country, where credit-ratings company S&P said it would cut Romania’s rating to junk in the face of more political upheaval. One of the poorest countries in Europe, Romania has run large budget deficits in recent years.

Dan has vowed to balance Romania’s budgets, clamp down on tax evasion and bring more accountability to the state.

“For many years there has been a distance between society and the politicians. People don’t think they’re part of decision-making in any way,” he said during a news conference in April. People think the government is “working not for society but for themselves.”

Corrections & Amplifications undefined Nicusor Dan’s hometown is Fagaras. An earlier version of this article incorrectly spelled it as Faragas in one instance. (Corrected on May 18)

Write to Thomas Grove at thomas.grove@wsj.com