Sanna Marin, who became the world's youngest prime minister in December, was formally chosen as chair of the Social Democratic Party (SDP) on Sunday morning.
Her predecessor as PM and party chair, Antti Rinne, has kept a low profile this year. He officially handed over the gavel to Marin at a party congress in Tampere, just a kilometre from her home.
After being elected unanimously, Marin, 34, thanked the delegates in a brief acceptance speech.
She and Antton Rönnholm, who was unanimously re-elected as party secretary, were handed bouquets as Queen's "Don't Stop Me Now" played in Tampere Hall.
Focus on education, R&D
During a longer policy speech on Saturday evening, Marin said that the main priority for the party in the upcoming government negotiations would be bolstering employment in an equitable manner. She also promised to focus on education, including an extension of compulsory schooling, as well as research and development work.
Marin's role as party leader has in effect been certain since late last year, when she suddenly replaced Rinne as prime minister following an uproar over a protracted labour dispute. At that point Marin was narrowly elected by the party council over parliamentary delegation chair Antti Lindtman by a vote of 32-29.
Further to the left
Rinne, 57, a former labour union boss, served two three-year terms at the party helm, but stayed out of the spotlight since Marin's ascension.
She is seen as taking the SDP further to the left, leading the party to become the nation's most popular with more support from women and younger voters.
She is also credited with leading Finland through the coronavirus crisis soon after taking office, with the country suffering far fewer deaths and less economic damage than most of its neighbouring countries.
Marin previously led the party on an interim basis in late 2018 and early 2019 while Rinne was seriously ill.
The convention also elected three deputy chairs out of six candidates.
They included two cabinet ministers, Timo Harakka and Ville Skinnari, three MPs (Aki Lindén, Niina Malm and Matias Mäkynen) and a union official, Jaana Ylitalo.
In a surprise result, first-term MP Malm edged out Minister of Transport and Communications Harakka for one of the positions. The other two posts went to Skinnari and Mäkynen.
14:35 Updated with new deputy chairs.