Dan, a 55-year-old mathematician and anti-corruption campaigner, won 54 percent of the vote, according to final results.
His victory over Simion, a vocal admirer of US President Donald Trump and leader of the far-right Alliance for the Union of Romanians (AUR), was welcomed by EU leaders as a sign of Romania’s continued alignment with Western democratic values.
Dan campaigned on a platform of rooting out corruption, maintaining support for Ukraine, and keeping Romania firmly anchored in the EU, the Reuters news agency reported.
Romania, alongside Poland, has served as a key logistics hub for Western military aid to Ukraine, it noted.
During the election campaign, Simion, 38, opposed military assistance to Ukraine and criticised the EU, stoking concerns in Brussels about a possible shift away from the European mainstream, according to reports.
His surge in support during the first round earlier this month contributed to the collapse of Romania’s pro-European governing coalition.
'Long live free Romania': Polish PM
Polish Prime Minister Donald Tusk was among the first to congratulate Dan.
"Congratulations Nicușor Dan," Tusk said on X. "Long live free Romania!"
European Commission President Ursula von der Leyen wrote: "The Romanian people have turned out massively to the polls. They have chosen the promise of an open, prosperous Romania in a strong Europe."
European Council President Antonio Costa also welcomed Dan’s election, saying: "From city hall to the table of the European Council. This is a strong signal of Romanians' attachment to the European project."
Moldovan President Maia Sandu described the result as "a step forward for democratic values and our shared European path."
Dan’s win comes amid broader concerns across the EU over rising nationalist sentiment.
Analysts warned that a Simion victory could have risked isolating Romania on the international stage and destabilising NATO’s eastern flank at a time of heightened tensions due to Russia’s ongoing war in Ukraine, according to Reuters.
French President Emmanuel Macron and German Chancellor Friedrich Merz also congratulated Dan.
"Despite numerous attempts at manipulation, Romanians tonight chose democracy, the rule of law, and the European Union," Macron wrote on X on Sunday, posting in Romanian.
Sunday's vote followed the annulment of the initial presidential ballot nearly six months ago amid allegations of Russian interference in favour of far-right candidate Călin Georgescu, who was consequently barred from running again.
Simion’s campaign was widely seen as part of a broader test of Trump-style nationalism in Europe, according to Reuters.
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Source: Reuters, IAR, PAP