Bassist Rayna Foss-Rose left the band after this album was recorded; she was replaced by Nadja Peulen, who had already previously replaced her for Coal Chamber's tours in 1999 during Rayna's pregnancy. This was the last studio album from Coal Chamber before they decided to split up due to musical differences which were creating tension between the band members. Dark Days is often regarded as the band's most aggressive and heaviest album; while past Coal Chamber albums had softer songs scattered throughout them, Dark Days stays mostly aggressive all the way through. Dark Days mostly combines the styles from the band's debut album with their second album Chamber Music, mixing the nu metal and alternative metal elements with the gothic metal elements from Chamber Music. Dark Days received mixed reviews from music critics but was more popular with fans.
On their last show, guitarist Meegs Rascón accidentally hit vocalist Dez Fafara on the head with his guitar, with Dez walking off stage only to reappear claiming that this was to be Coal Chamber's last show. Dez then released Giving the Devil His Due which was a collection of unreleased tracks, remixes, and demos by Coal Chamber. Afterward, he went on to start the band DevilDriver.
"Fiend" would be the album's only single. Its music video found airplay on Uranium, which also featured an interview with the band and the song Glow was also featured on the Scorpion King soundtrack.