Helsinki: A 34-year-old transport minister and MP has been tapped to become Finland's youngest prime minister ever and its third female government leader.

Finland's ruling Social Democratic Party council voted 32-29 late on Sunday, local time, to name Sanna Marin to take the government's top post from rival incumbent Antti Rinne.

Sanna Marin smiles after she won the SDP's prime minister candidate vote against Antti Lindtman in Helsinki, Finland, on Sunday. Credit:Lehtikuva/AP

Having emerged as the largest party in the April election, the Social Democrats can appoint one of their own to the post of prime minister in the Nordic nation of 5.5 million.

Marin has been the party's vice-chairwoman, an MP since 2015 and served as until this week as the minster for transport and communications. She will be the world's youngest sitting leader, followed by Ukraine PM Oleksiy Honcharuk, 35, and North Korea's Kim Jong-un, 36. New Zealand PM Jacinda Ardern was elected when she was 37.