Finland’s centre-right former prime minister Alexander Stubb will become the next president after winning an election runoff with rival Pekka Haavisto in the country’s most high-stakes presidential election in a generation. Stubb, of the National Coalition party, declared victory on Sunday night and Haavisto, a former foreign minister and a member of the Green party running as an independent, congratulated him. With 99.4% of votes counted, Stubb had 51.6% of the vote to Haavisto’s 48.4%. Nearly half (about 46%) of voters who were permitted to take part in early voting did so, according to official data. Stubb, 55, said the role would be “the greatest honour” of his life. He added: “The task of the president of the republic is bigger than a person.” Conceding just before 9pm local time, having already fallen behind in early voting, Haavisto shook hands with Stubb, thanking him and wishing him “success in your work”. Stubb, 55, was born in Helsinki and has been a member of the European parliament, a member of Finland’s parliament, prime minister between 2014 and 2015, and a minister. Outside politics he has worked as vice-president of the European Investment Bank and as a professor at the EU University in Florence, and is a keen triathlete. He has two grown up children with his British-Finnish wife, a lawyer, Suzanne Innes-Stubb. He will succeed the two-term president Sauli Niinistö, who oversaw his country’s accession to Nato. In the first-round ballot two weeks ago, Stubb and Haavisto won 27.2% and 25.8% of the votes respectively, leading a field of nine candidates including Jussi Halla-aho, of the far-right Finns party, who came third. In the frantic final days of campaigning, the candidates’ personal lives and attitudes to nuclear weapons came into sharp focus. Haavisto, bidding to be the country’s first Green and first gay president, questioned why his sexuality had been in the spotlight in recent days. The 65-year-old said he had been surprised by the way his sexuality had become an issue of public interest in the second and final round and said journalists, particularly those from the national broadcaster, Yle, had been “triggering” discussion around it. The Finnish president is the head of state and commander-in-chief of the army and responsible for foreign policy in cooperation with the government. International security and defence have been a high priority for Finnish voters amid accusations of Moscow instigating a “hybrid operation” on Russia and Finland’s shared border, leading Finland to temporarily close the frontier in its entirety. Stubb has described foreign policy and security as existential issues for Finland. He told the Guardian earlier in the campaign: “For Finland, foreign policy, security policy, is existential.” As well as public debate of Haavisto’s sexuality, nuclear weapons were also a central topic. While Stubb is in favour of allowing nuclear weapons to be transported through the country, Haavisto, who previously worked as a UN peace negotiator, wants to maintain Finland’s nuclear weapons ban.