Poroshenko arrived in Helsinki Tuesday from the Estonian capital Tallinn following a meeting there with Estonian President Kersti Kaljulaid on Monday.
The planned agenda for Tuesday's talks between Poroshenko and Niinistö was reported to focus on the Ukraine conflict and the implementation of the Minsk Agreement, as well relations between the EU and Ukraine.
Contacts with Russia and Ukraine
Niinistö has maintained regular contacts with both Russian President Vladimir Putin and President Poroshenko. The two last met at the NATO Summit in Warsaw in July 2016. Putin is due to visit Finland at Niinistö's invitation later this year to take part in observances of Finland's 100th anniversary of independence.
During Poroshenko's visit, government officials will sign a memorandum of understanding between Finland and Ukraine on cooperation in the energy sector.