Born in the town of Espoo, Finland, Janne Wirman began playing the piano at the age of five. For most of his early life he focused his style on jazz, switching his main interest to heavy metal music once he joined the metal band Children of Bodom in 1997.
He graduated from the Helsinki Pop & Jazz Conservatory at the age of sixteen and was subsequently invited by Jaska Raatikainen to join Children of Bodom, due to their previous keyboardist - Jani Pirisjoki - being fired from the band. Janne was the deciding factor for them to truly begin their professional career. Not only did he bring his talent to the band, but after a single practice he also became able to play in perfect synchrony with lead guitarist and vocalist Alexi Laiho. This synchrony can be better observed on their live performances, or on the Tokyo Warhearts album, on the tracks Bed of Razors and Downfall.
His primary influence is keyboardist Jens Johansson from Stratovarius (also played with guitar virtuoso Yngwie Malmsteen and Dio) from whom he has adopted the style of playing his keyboard tilted forward.
In the year of 2000 Janne assembled progressive metal band Warmen as his main side-project. The band's second album - Beyond Abilities - continued with the presence of Janne's brother Antti Wirman.
In the same year, Jens Johansson was asked by heavy metal band Masterplan to play on their debut album, but since he was already busy with other projects, he referred them to Janne instead. Thus, in early 2002, Janne took part in the recording of Masterplan's self-titled debut album. The band proceeded to offer him a permanent position, but Wirman opted to continue playing with Children of Bodom. Masterplan released their album and gave credit to Janne's work on the CD's booklet. The band's keyboard player Axel Mackenrott - hired after Janne's decline to enter the band - appeared on all of the promotional pictures, and was officially credited as Masterplan's keyboardist.
To record with Warmen, Janne built the Warmen Productions Studio (now named Beyond Abilities). This studio has also served for the recording of Kotipelto's keyboard tracks, part of Ensiferum's Iron album and Sinergy's fourth album.
Janne has had bad experiences with sponsor deals. He had deals with both Roland Scandinavia and Korg in the past and was promised new equipment, but he never received anything. On the back of Warmen's second album it reads: "No Roland or Korg products were used".
Janne was originally just supposed to play a few shows with Children of Bodom, but they grew to like him. On the Chaos Ridden Years documentary, Alexi Laiho says, "But it was the first time I saw the guy drunk, and that's when I knew he was the fucking man." Janne stayed with the guys, but said he felt like a real member of the band around the time of the recording of his second album with them.