He studied vocals at the pop/jazz conservatory in Helsinki, briefly singing for an amateur cover band named Filthy Asses. In summer of 1994, he applied to Stratovarius, who were looking for a singer at the time, and was accepted. His arrival corresponds closely with the band's rise to international fame. The first album he recorded with the band was Fourth Dimension, in 1995. Stratovarius has then become a top name in the European heavy metal scene, recording seven more albums and performing in numerous notable rock festivals.
In late 2003, Kotipelto split from Stratovarius after intra-band disagreements, notably with guitarist Timo Tolkki. After much turmoil throughout 2004, he rejoined the band in January 2005, recorded the album Stratovarius, and performed live on tour that covered North America, South America, Europe and Asia. In 2008, Timo Tolkki made public that he and Timo Kotipelto had arguments but Koltipelto never really left the band and the announcement that he left was part of a big publicity stunt.