After more than a decade under the leadership of popular President Sauli Niinisto, his successor is now set to be decided on February 11 when the two top vote-getters face off.
The centre-right's Stubb achieved 27.3 per cent of the vote in Sunday's election while the Green's Haavisto received 25.8 per cent, Finnish broadcaster Yle projected with most of the votes counted.
Parliamentary Speaker Jussi Halla-aho and former EU commissioner Olli Rehn were well behind with about 16 per cent each.
A provisional final result should be issued later in the evening.
Finnish voters were called to the polls on Sunday to elect a successor to Niinisto, who was not allowed to run again after two six-year terms in office.
In Finland, the president is directly elected by the people.
One of the president's most important tasks is to decide on foreign and security policy together with the government, appoint the government, and approve laws.
Stubb, prime minister from 2014 to 2015, and Haavisto were the favourites going into the first round.
Following the run-off, the new president is due to take over from Niinisto on March 1.
