In her earlier days, Olzon took singing lessons at the Copenhagen Music Conservatorie, in Helsingør, Denmark, with a private teacher.

[2] Before singing, Olzon has worked in a factory, in a hamburger restaurant, as a waitress, as a veterinarian assistant, in a number of offices and as a hair dresser.

[3][non-primary source needed] She has also studied musical artist education, psychology, project management and leadership and organization.

[3] Olzon then joined Alyson Avenue, at first only as a studio singer, but later as their leading lady, replacing the male vocalist.

Olzon officially joined Nightwish as their new lead singer in early 2007, chosen from about 2,000 applicants of which 10 made it to prove their place in front of the band.

Olzon's demo was one of the first that Nightwish received, although she was originally denied the position, as band leader Tuomas Holopainen was concerned about the fact that she had a young son.

Her identity was kept secret by various methods, including pretending to be Ewo's "Swedish cousin" at a Tarot concert, until she was eventually announced as the new Nightwish singer on 24 May 2007.

It was originally scheduled for release on 30 May but this was changed due to a leak on a British music download site.

On 13 June Nightwish released the title, Dark Passion Play, and artwork to the new album on their official website, as well as the name and the cover of the second single (this time CD), "Amaranth".

[7] The Dark Passion Play tour thus started, visiting the United States, Canada, most of Europe, Asia, and Australia.

"[15] In a 2021 interview with Blabbermouth.net, Olzon revealed that she wanted the band's tour dates pushed back due to her pregnancy, but Holopainen denied the request.

[16] Following her departure from Nightwish, Olzon began writing and recording material for a future solo album.

[21][non-primary source needed] In a June 2015 interview, Olzon said she had plans for a future second album, but details are still being discussed with her new label.

[25] Olzon announced on 29 August 2017 that she would be collaborating with former Sonata Arctica guitarist Jani Liimatainen for a project known as The Dark Element.

[28] Olzon has played with several bands, in studio and live, including Brother Firetribe on the song "Heart Full of Fire" from the album of the same name in 2008, The Rasmus on the single "October & April" in 2009, Pain on the song "Follow Me", "Feed Us" from Cynic Paradise in 2008 and Black Mount Rise on the single "Apart & Astray" in 2015.

On 13 August 2009, Olzon sang two Nightwish songs, "Kuolema Tekee Taiteilijan" and "Meadows of Heaven", with the Swedish Radio Symphony Orchestra, at the Suomi Safari – the event was in celebration of Sweden and Finland relations.

[31] Along with the several popular Finnish musical artists, Olzon performed their own covers of songs from various genres, with one singer being dropped out of the competition each week by televote.