When Finland’s new prime minister is sworn into office on Tuesday, 34-year-old Sanna Marin will become the youngest sitting leader in the world, the youngest prime minister in Finland's history and only its third ever female premier.

Chosen by her Social Democratic party on Sunday and affirmed in the position by a parliamentary vote on Tuesday, she will lead a coalition government composed of five parties all headed by women.

In a remarkable moment for Finnish politics, almost all of the five coalition party leaders are under the age of 40, with the only exception being Swedish People’s Party leader and the current justice minister Anna-Maja Henriksson, who is 55.

Katri Kulmuni, leader of the Centre Party and minister of economic affairs, is 32; Maria Ohisalo, leader of the Green Party and interior minister, is 34; and Li Andersson, chair of the Left Alliance and minister of education, is 32.

Ms Marin replaces Antti Rinne, who resigned last week after he lost the confidence of a key coalition partner just six months after he became prime minister.

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Ms Marin said on Twitter after she was sworn in: “Finland will not be finished in four years, but it can get better. That's what we're working on.

"I want to build a society in which every child can become anything and in which every human being can live and grow old with dignity.”

She was born and raised in Helsinki by her mother and her mother’s female partner, in what she calls a “rainbow family”.

Ms Marin credits the Finnish Welfare State and her “demanding teachers” for getting her through her academic years, and remains a strong advocate of the welfare system.

She is the first person in her family to graduate both high school and university, where she obtained a masters degree in Administrative Sciences in 2017.

As a teenager, she worked in a bakery and distributed magazines to earn pocket money, and worked as a cashier after graduating high school.

Her involvement in politics began in her early twenties when she joined the Social Democratic Youth and served as its vice president from 2010 to 2012.

After that, she won a seat in the city of Tampere and became a council leader at age 27, cementing her career in politics.

Finland's new prime minister Sanna Marin formerly served as transport minister (AFP/Getty)

She quickly rose through the ranks and became an MP in 2015. Four years later, Ms Marin became the minister of transport and communications.

When she was chosen to be prime minister, questions were raised about her suitability because she has a 22-month-old daughter with her husband.

Dismissing those concerns, Ms Marin said: “I have never thought about my age or gender. I think of the reasons I got into politics and those things for which we have won the trust of the electorate.”

Ms Marin takes office at a tumultuous time in Finland, with a number of strikes and the halting of production at some of the country’s largest companies looming on the horizon.

Strike action began on Monday involving 100,000 workers from a number of industries, including fuel production, pharmaceutical companies, mines, and technology companies, and is planned to continue for three days.

According to Finnish newspaper Yle, it is one of the biggest strikes in recent years and has the potential to impact the availability of some medications and the distribution of oil.

Despite the challenges she faces, Ms Marin has received an outpouring of support from other leaders.

Petteri Orpo, chair of the opposing National Coalition Party, said: "A historic day: The world gets the youngest sitting prime minister and Finland gets a government in which all of the party leaders are women.