Former Foreign Minister Pekka Haavisto, of the center-left Green League, was lagging behind at 48.1% of the vote, official data published by the Justice Ministry showed.
Back in the first round on January 28, Stubb received 27.2% of votes and Haavisto - 25.8% of votes.
While advocating for different domestic policies, both candidates support sealing the border with Russia, ramping up sanctions against Moscow and assisting Kiev militarily - despite the fact that the nation's economy has suffered significantly from a major downturn in trade with its eastern neighbor over the past two years.