[2] Lassila became one of the original founding members of "Black Water" (early Stratovarius name), the others being bassist John Vihervä and guitarist Staffan Stråhlman.
In 1985, Stråhlman quit the band and Lassila approached guitarist Timo Tolkki to fill in the position.
[2] In 1998, he joined the Finnish band Conquest, led by Peter James Goodman and played drums in their first album Worlds Apart (released in 1999) and also in a tribute (with Conquest) to Iron Maiden, playing in the song "The Evil That Men Do" on the tribute album Slave to the Power which was released in 2000.
[5] On 28 October 2013 it was announced that Tuomo Lassila will be the drummer for the second album of his former Stratovarius bandmate Timo Tolkki's metal opera Avalon.
[6] A few weeks later, on 23 November, it was also announced that Antti Ikonen is also joining the project, being the first time the three original members of Stratovarius reunite to make music in nearly in 20 years.