Immortal was formed by bassist/vocalist/drummer Abbath Doom Occulta (Olve Eikemo) and guitarist Demonaz Doom Occulta (Harald Nævdal). The core duo was joined by a string of drummers who typically lasted for one album and were often hired for touring purposes only while Abbath took care of the drumming on albums. In 1996 they however settled on Horgh (Reidar Horghagen) for their fourth album "Blizzard Beasts" and the duo became a trio
In 1997 Demonaz developed a tendinitis to his arm, which led to him being no longer able play guitar in the style required to perform with Immortal. Hence Abbath changed from bass to guitar and also became the main songwriter in the band. Demonaz however remained a full member of the band and focused on writing the lyrics and managing the band. Following the release of "At The Heart Of Winter" in 1999, Iscariah (Stian Smørholm) joined the band as a touring bassist.
In 2003 Immortal split up, but was reformed in 2006 and the band started to perform live again in 2007. This time the live bass was played by Apollyon (Ole Jørgen Moe). "All Shall Fall", their first new album after the split-up, was released in 2009.
In December 2014 it was reported that the three band members (Eikemo vs. Nævdal/Horghagen) had ended up in a legal feud over the rights for the Immortal band name.
In March 2015 Abbath made an announcement that Immortal was put to rest for the time being and he would continue making music and performing as "solo" artist using his own name, Abbath. In August of that year, Demonaz and Horgh announced that they were continuing Immortal on their own.
In 2018, three years after the name dispute and nine years after their previous full-length, Demonaz and Horgh released a new Immortal album "Northern Chaos Gods".