Ofermod were formed in 1996 by Nefandus drummer, backing vocalist and lyricist Mika "Belfagor" Hakola. The band recorded the "Mystérion Tés Anomias" single in Tore "Necromorbus" Stjerna's Necromorbus studio in January 1998 and released it through Pounding Metal Productions.
In 2000, Belfagor retired from his musical activities to concentrate on his occult studies and practices. In 2003, while in prison, Hakola started composing again. In 2004, he was joined by singer Nebiros again, and they recruited drummer Tore "Shiva" Stjerna, who had produced the Mystérion Tés Anomias single. After he served another prison sentence, Hakola got in contact with guitarist Atum, and through him with bassist Tehôm. In December 2004, the band recorded two songs for the Mystérion Tés Anomias re-release through Norma Evangelium Diaboli; on the re-release, Hakola used the new pseudonym "Michayah", and Nebiros called himself Leviathan.

The band's first album "Pentagrammaton", which was supposed to feature Moloch of Teitanblood sharing vocals with Nebiros and "mark the ten year anniversary of Ofermod" in 2006, was "partly finished in late 2005/early 2006", but delayed because "Michayah was sent to prison, for assault, robbery and a few other incidents, in early march 2006". He was released in August 2006, but sentenced to serve more time the same year, "due to new acts of violence". Pentagrammaton was therefore further delayed until 2007.
The album remained unreleased because "obviously the forces of chaos did not want this album to be released". Belfagor took time to solely re-work the material, which was produced by Marduk bassist Magnus "Devo" Andersson and released under the title "Tiamtü" in 2008.

After that the band realized "Thaumiel" in 2014 and "Sol Nox" in 2017.
After the 2019, the band lost two members and now release the fifth album "Mysterium Iniquitatis".