His parents were entrepreneur Pentti Holopainen (1940–2021), and Kirsti Nortia-Holopainen, a former music and English teacher in a small elementary school.

[9] Originally aspiring to be a biologist,[9] Holopainen had no interest in metal until his school foreign exchange partner took him to see Metallica and Guns N' Roses in America, and he became hooked.

[2] He was then conscripted for the Finnish Army, where he managed to earn a position as the clarinet player of the military band, which spared him from gun-related activities.

He asked Emppu Vuorinen and classmate Tarja Turunen to join what was then an acoustic project,[16] with music he wrote during his time in the army.

After the last concert (a filmed show in Hartwall Areena, Finland which was featured on the End of an Era DVD in 2006), in October 2005, Nightwish gave vocalist Tarja Turunen a letter explaining her dismissal from the band.

In 2006, Holopainen went through a dark period filled with anxiety and depression, made worse by rumours about himself and Nightwish in the tabloids every day.

After heavy metal singer Timo Rautiainen's break up of Trio Niskalaukaus, he published his first solo album titled Sarvivuori with a crew gathered from different bands, including Holopainen on keyboards.

Early the next year, For My Pain... announced that they would soon start recording the successor to Fallen, but it was reported in the same autumn that the album once again was postponed.

In April 2007 Holopainen collaborated with fellow Nightwish member Marko Hietala to write a theme song for the Finnish film Lieksa!.

[20] On "While Your Lips Are Still Red", in addition to Holopainen on piano, Marko Hietala performs vocals and acoustic bass guitar, and Jukka Nevalainen plays drums.

In 2007, Holopainen played keyboards with Finnish punk band Kylähullut on their EP Lisää persettä rättipäille.

[21] The new vocalist for Nightwish was revealed in May 2007; Swede Anette Olzon, who appears on Dark Passion Play, released in late August of the same year.

[22] Holopainen stated on his website, The Escapist, that he planned to devote his time completely to songwriting for the project in Feb–April 2013 after the Nightwish Imaginaerum tour.

[23] In a November 2015 interview, he revealed plans to release a book with short fantasy and horror stories influenced by Neil Gaiman and Stephen King.

[24] Ex-singer of Visions of Atlantis, Nicole Bogner, also acknowledged that Nightwish had greatly inspired the band, especially for their first album.