In 1987, Tiamat was formed in Täby, Sweden as Treblinka. Treblinka released two demo tapes, "Crawling in Vomits" and "The Sign of the Pentagram", before changing their name and releasing the 1990 debut full-length Sumerian Cry.

Tiamat was originally a black metal band in the vein of other early 90's innovators like Samael and Mayhem, but influenced by the likes of Mercyful Fate and Candlemass they gradually dropped their extreme metal stylings in favour of a psychedelic/progressive heavy/doom metal sound in the mid 90's.

The very Pink Floyd inspired, though within metal then quite innovative, use of keyboards and acoustic guitars, peaked with their 1997 A Deeper Kind of Slumber, now nearly completely lacking any semblance of metal. After this, the band changed to a gothic rock/metal style that their last 3 albums have stuck fairly close to.

Their commercial "break-through" and most well-known album is 1994's Wildhoney, an album that made Tiamat one of the most popular European metal bands, and that is arguably the best representation of Tiamat's overall sound, containing both the death metal-esque vocal stylings of old and the newer psychedelic/goth rock-influenced sound.