By Essi Lehto

HELSINKI (Reuters) -Finland's former Prime Minister Sanna Marin, who narrowly lost an election in April, stepped down on Friday as chair of the centre-left Social Democrats, hoping to take the focus off her personal life after an often turbulent four years at the helm.

Marin, who had announced her intention to quit soon after the election loss, was the world's youngest prime minister when she took the post in 2019 aged 34, attracting attention around the globe and helping lift Finland's profile.

After leading the country through COVID-19 lockdowns and the ensuing economic turmoil, Marin became a vocal supporter of Ukraine after Russia's invasion last year and successfully pushed to end Finland's military non-alignment in favour of NATO membership.

She chaired her party's conference for the last time on Friday and in a brief speech, she reiterated her criticism of Finland's eastern neighbour.

"Russia and its representatives must be held accountable for the illegal crime of aggression, war crimes and the consequences of war," Marin said.

"In addition to Finland's steadfast support for Ukraine and the Ukrainians, we must also send a strong message of hope for the reconstruction of the country, for a European future."

Marin, now 37, has appeared on the covers of Vogue and Time Magazine, has a million followers on Instagram and is considered by fans around the world as a millennial role model for progressive leaders.

But at home, voters concerned with issues like immigration and a growing public deficit in April handed Marin a narrow defeat to the right wing National Coalition and the far-right Finns party, triggering the government's fall.

She weathered several publicity storms while in office, including over her nightclubbing during the pandemic, hosting private parties at her official residence and voluntarily taking a drug test after a party video was leaked to the media.

The drug test was negative, Marin announced, and she apologised to Finns when a picture from a party at the prime minister's seaside residence showed two well-known female influencers covering their bare breasts with a "Finland" sign.

After her election loss, Marin said she looked forward to a quieter life and later also announced a divorce from her husband.

Entering the stage on Friday to the beat of Aretha Franklin's "Respect", Marin thanked her party for its support.

Marin handed over the reins to Antti Lindtman, 41, who lost the leadership election to her in 2019 and thanked her for taking their party and Finland through "exceptionally difficult times".

"You showed leadership both in Finland and abroad in a way we are very proud of," Lindtman said, looking at Marin who smiled through tears on the front row.

Marin remains a member of parliament and has also enlisted as a public speaker with a U.S. agency and founded a consultancy with her former assistant.

(Reporting by Essi LehtoEditing by Frances Kerry and Mark Potter)