In October 2018, the chairman of the Green League Touko Aalto announced that he is resigning from his post, citing depression and fatigue. The decision prompted an immediate leadership election, with the goal to elect a temporary chairman to lead the party into the 2019 parliamentary elections and until the next party convention.
As many members of the party called for more prominent and experienced politicians to take part in the election, Haavisto announced his candidacy. On 4 November 2018, he defeated MP Outi Alanko-Kahiluoto in a leadership election and was thus chosen to lead the party.