Initially, the band played straightforward black metal under the name Treblinka. After having recorded the album Sumerian Cry in 1989, vocalist/guitarist Johan Edlund and bassist Jörgen Thullberg parted ways with the other two founding members, and subsequently changed the name to Tiamat. The Sumerian Cry album included re-recorded Treblinka songs and was released in June 1990.
After the debut, Edlund's leadership would modify the band's style with influences ranging from Black Sabbath, Mercyful Fate, Candlemass, Pink Floyd and King Crimson, with Sumerian lyrical themes. Polish guitarist Waldemar Sorychta would produce and contribute instrumentation to many of the band's albums, as well as those by Tiamat's own tour and labelmates, including Moonspell, Rotting Christ, Lacuna Coil and Samael.
1994's critically acclaimed Wildhoney mixed raw vocals, slow guitar riffs and synthesizer sounds which sounded different from other extreme metal bands active at that time. An almost continuous forty-minute piece of music, Wildhoney led to the band's appearances at the Dynamo and Wacken Open Air heavy metal festivals in 1995. The group would play a second gig at Dynamo two years later.
Upon the release of A Deeper Kind of Slumber (1997), Edlund relocated from Sweden to Germany and declared himself the only permanent member of the band; all albums that would follow would cement the band into a more gothic rock sound, quite different from the extreme music they did in the years before, with recent albums showing a Sisters of Mercy and Pink Floyd influence.
The band signed to Nuclear Blast in June 2007, and released their ninth album Amanethes on April 18, 2008.
Their song Cain was also featured in the video game Vampire: The Masquerade – Bloodlines.
The band's tenth full-length studio album, The Scarred People, was released on November 2, 2012 through Napalm Records.