Her vocal style is notable for both shrill and deep tones, and also the use of multitracked vocals, with different uses of pitch-shifting technology on each track, creating an intricate and mysterious effect. Visually, Andersson employs the use of masks, face and body paint, intricate costumes, and other theatrical elements in photo shoots, videos and live performances, during which she often performs behind a gauze screen that partially obscures her from view.
While The Knife was on hiatus, Andersson released her self-titled solo debut album Fever Ray digitally on 12 January 2009 and physically on 18 March 2009 via Rabid Records, preceded by its lead single "If I Had a Heart", released digitally on 15 December 2008. The song was later used in the 31 July 2011 episode of American television series Breaking Bad, as well as becoming the main title music for the Canadian-Irish historical drama television series Vikings, which premiered on 3 March 2013.
In 2009, Andersson composed the soundtrack to Dirty Diaries, a collection of feminist pornographic short films. In a review of the collection, Swedish newspaper Smålandsposten described the soundtrack as appropriate to the film, though repetitive.
Contrary to a statement from the film's director, Andersson did not make a cameo appearance in the 2011 film Red Riding Hood. However, the soundtrack features the exclusive track "The Wolf", which Andersson co-wrote with her band members, as well as "Keep the Streets Empty for Me".
In 2005, Andersson supplied vocals on the track "What Else Is There?" by Röyksopp on the album The Understanding. She also appeared in the video for that single, but not as the vocalist, who was portrayed by a model. In 2008, Andersson provided vocals for the dEUS song "Slow" from the band's Vantage Point album. Andersson was featured on the tracks "This Must Be It" and "Tricky Tricky" again by Röyksopp, appearing on their 2009 album Junior.
Andersson was born on 7 April 1975 in Nacka, Sweden. While both Karin and Olof are hesitant to give interviews, Karin takes part in them more frequently than her brother. On the occasions they do consent to interviews, they often stick to topics concerning their music, influences and public image, avoiding talking about their personal lives. Andersson is married to Kent Peter Kristian Andersson and has two children, though the first names of her children are not publicly known, to protect the privacy of her family.