Hietala joined Nightwish in 2001 when Tuomas Holopainen and the band's manager called him and said that there would be a place in the band for a vocalist and a bass player. Century Child was his first Nightwish album, following the departure of previous bassist Sami Vänskä. He was a prominent guest musician in Delain, a project involving many members of the gothic and symphonic metal community. He also participated in the recording of Invitation, by Altaria, providing backing vocals. Hietala has also been part of the bands Sinergy and Northern Kings.
