Sofi Oksanen was born and raised in Jyväskylä located in Central Finland. Her father is a Finnish electrician, her mother an Estonian engineer who grew up in Estonia during the Soviet period and immigrated to Finland in the 1970s. Oksanen studied literature at the Universities of Jyväskylä and Helsinki and later drama at the Finnish Theater Academy in Helsinki. Oksanen is actively involved in public debate in Finland and comments on current issues in her columns and various talk shows. She is a self-identified bisexual and has suffered from eating disorders. In 2009 she received an award from the organizers of Helsinki Pride for her activism on behalf of LGBT people in the Baltic states (Estonia, Latvia, Lithuania) and Russia.

Oksanen first became well-known for her novel Stalinin lehmät ("Stalin's Cows") (2003)., a story about a young girl's eating disorder and the image of Estonian women who had immigrated to Finland. It was nominated for the Runeberg Prize.

Two years later, she released her second novel Baby Jane (2005). about anxiety disorder as well as violence among lesbian couples.

Oksanen’s first original play Puhdistus (”Purge”) was staged at the Finnish National Theatre in 2007. From out of the play grew Oksanen’s third literary novel Puhdistus (2008). It ranked number 1 on the bestseller list for fiction in Finland when it was published.

The novel Purge won the Fnac prize in 2010, selected from some 300 works published in France amid positive reviews by French critics, it was the first time the prize had been awarded to a foreigner. The best selling novel is set to become a film in 2012, to be produced by Markus Selin.

Oksanen was awarded the prestigious Finlandia Prize (2008), the Runeberg Prize (2009) and the Nordic Council Literature Prize (2010) for Puhdistus.

In 2009, the largest daily Estonian newspaper Postimees named Sofi Oksanen Person of the Year; according to the editor-in-chief Merit Kopli the decision was unanimous. In 2010 the Estonian President Toomas Hendrik Ilves decorated Sofi Oksanen with the Order of the Cross of Terra Mariana IV Class.