The conservative favourite and former finance minister won 37% of the vote. Niinistö faces a February 5 runoff with another pro-euro candidate, Pekka Haavisto of the Greens Party, who took 19% of the vote.
Anti-euro candidates Paavo Vayrynen and Timo Soini dropped out of the race after the final tally.
While the president has little executive power beyond military and diplomatic affairs, it is a high-profile post and the strength of the pro-euro vote will ease pressure on the government to take a hard line against Brussels.
A euroskeptic leader may have forced Prime Minister Jyrki Katainen to demand stricter conditions on European bailout plans in the months ahead.
"This has significance. This has an impact on political discussions, as Europe is going through difficult talks on crisis management," said University of Helsinki professor Tuomo Martikainen. He and other analysts said Niinisto will likely win the second-round.
Favouring an internationalist approach
The presidential election comes 9 months after Soini's Finns Party made strong gains in a parliamentary election after a campaign that focused on criticising European bailout plans.
High taxes, combined with a lackluster economic growth outlook, fuelled criticism that Finland was helping some countries get an easy ride out of debt, while voters faced austerity at home.
Yet Sunday's result showed most voters would rather be represented by a more internationalist leader.
Soini was fourth with 9% of the vote. Analysts said his popularity may have been hit by racist comments by some party members as well as his own provocative style. Prospects of a Europe-wide recession are also making voters wary of choosing a president who does not support the government, they said.
Finland's government and the eurozone are expected to agree on Monday to new rules for a €500-billion bailout fund. Finland had been the sole objector to a proposed new majority voting system and a deal would remove an obstacle to the scheme's launch in July.
Niinistö, who has also worked for the European Investment Bank, reaffirmed his support for Finland's pro-Europe stance, saying: "The EU is an essential direction for us. We are European."
Both he and Katainen are members of the National Coalition party which represents conservative economic policy and liberal social values, although as president he is expected to renounce party affiliation.
Some voters said they were concerned last year's rise of the Finns Party, previously called the True Finns, had stirred feelings of xenophobia in a country where less than 5% of the population are immigrants.
"The political discussion has grown more conservative and xenophobic after the True Finns victory last year," said 29-year-old advertising manager Erik. He voted for Haavisto, the first openly gay presidential candidate.
Haavisto, voting with his partner in central Helsinki, said: "In one way I am a pioneer, but I think the Finns are very tolerant people and they accept people for who they are."
President Tarja Halonen was elected as the country's first woman president in 2000 and re-elected in 2006. She steps down having served 12 years, the maximum term in office.
