The leader of the eurosceptic Finns Party is to step down in June when the party votes for a new chairman - leaving no clear leader to take over.
Timo Soini, who is foreign minister, changed Finland's politics by hugely increasing his party's popularity in two successive elections and entering the government for the first time in 2015.
The 54-year-old, who co-founded the party, previously known as the True Finns, said on Sunday that after two 10-year terms as chairman it was time to go.
However, he said that he would like to remain foreign minister until the current three-party coalition's term is due to end in 2019.
The Finns Party's popularity has fallen in polls to about nine per cent support, from 18 per cent in the previous election.