Their first several albums were a confusing mish-mash between black metal, goth and death. The Astral Sleep (1991) made little attempt at correcting this. It also saw Thomas Petersson take over the guitar slot. Clouds (1992) featured Johny Hagel (ex-Sorcerer; bass) and Kenneth Roos (keyboards) joining. The follow-up Sleeping Beauty - Live Israel (1994) followed up as their first live effort.
The transformation was finally complete by Wildhoney (1994), where the death metal vocals were mostly gone, and the Pink Floyd influences were found. This album also saw more membership shifts, with Roose gone, as well as Hagel leaving to join the Cemetary offshoot Sundown, and Lars Skold (drums) joining. The follow-ups of Gaia EP (1995), featuring Lars Skold taking over the drums, the self-explanatory The Musical History Of Tiamat (2CD compilation; 1996) and A Deeper Kind Of Slumber (1997) with Anders Iwers on bass followed the same path. These albums were considered excellent by many critics, even if public reaction was mixed. A Deeper Kind Of Slumber saw Anders Iwers (ex-Cemetary) join on bass, while Thomas Petersson returned (he was absent since the completion of Clouds).
The long-awaited Skeleton Skeletron was released in 1999 coming across as a fresh change in their style by being more goth and more heavy; over-all more diverse then the past albums. The album also saw the departure of Petersson, but would be back for Judas Christ (2002) and Prey (2003), two albums that collowed the same musical pattern.
The compilation Commandments (2007) and The Ark of the Covenant - The Complete Century Media Years boxed set (2008) would follow.
On August 10, 2008, Thomas Wyreson quit to spend more time with family.
Their song Cain was also featured in the video game Vampire: The Masquerade - Bloodlines.
Edlund then embarked on a solo career outside of his Tiamat duties, releasing an album under the name Lucyfire, called This Dollar Saved My Life At Whitehorse. Lucyfire has proven to be a much brighter, rock-oriented and considerably less metal outfit than Tiamat, but this influence has not yet appeared in the Tiamat albums.
The band signed to 'Nuclear Blast' in June 2007, and released Amanethes on April 18, 2008, an album that boasted the return of Thomas Wyreson (guitars/vocals (backing)). Roger Öjersson (guitars (lead)/keyboards/mandolin/vocals (backing)) would be the new man of note for The Scarred People (2012).