With all ballots counted on January 28, Niinisto had 62.7 percent of the vote, far more than his top rival, Pekka Haavisto of the Greens, with 12.4 percent.
Euroskeptic politicians Laura Huhtasaari of the nationalist Finns Party and independent Paavo Vayrynen scored less than 7 percent each against the pro-EU Niinisto. Turnout was 69.9 percent.
"I am very surprised at this kind of support. I must think hard how to be worthy of it," the 69-year-old Niinisto told reporters.
In his first six-year term, Niinisto was seen as playing a key role in maintaining relations with Moscow, even as Finland supported Western economic sanctions against Russia over its 2014 annexation of Crimea from Ukraine and its support of separatists in eastern Ukraine.
Finland shares a 1,340-kilometer border with Russia and has fought wars against its much-larger neighbor over the centuries.
It has developed closer ties with NATO but has not joined the alliance as it attempts to avoid antagonizing Moscow.
Comment: See:
- Support for NATO on the decline: Nearly 60% of Finns say 'no thanks' to NATO membership
- Finland would rather be friends with Russia than members of NATO, says President Sauli Niinistรถ
"I think there is no reason to seek [NATO] membership as long as circumstances are as they are now," Niinisto said. "But if there are crucial changes in the environment, then we might be in a different situation."
In Finland, the president plays an important role in foreign and defense policy, although the position has become largely ceremonial over recent decades.
Comment: While much of the Western world is plagued with anti-Russian hysterical propaganda, taking a constructive stance towards friendly relations with Russia is a bold move but also the most reasonable one: