The conception of Sinsaenum can be traced as far back as 1998, when French guitarist Frédéric Leclercq (best known as the bassist of English power metal band DragonForce) began writing a number of death metal songs. After recruiting fellow French guitarist Stéphane Buriez of Loudblast for the project, Leclercq was contacted by American drummer Joey Jordison (known for his work with Slipknot, then a member of Scar the Martyr and later of VIMIC) with the intention of working together, who later became involved in the project.Jordison proposed the band name Sinsaenum, which is a modified portmanteau of the words "sin" and "insane". The trio later added Attila Csihar of Norwegian black metal band Mayhem and Sean Zatorsky of American death metal group Dååth as dual lead vocalists, in addition to Seth guitarist Heimoth on the bass to complete the lineup. The formation of the band was officially announced on May 20, 2016.

Sinsaenum released its self-titled debut extended play on June 6, 2016, featuring the exclusive track "Death Is the Beginning" and album track "The Forgotten One". After a music video for the song "Splendor and Agony" the band's debut full-length album Echoes of the Tortured was released by earMUSIC on July 29, 2016.A lyric video was later released for "Anfang des Albtraumes" in August.

In early 2017 the band entered the studio again to begin the process of writing and recording what they dubbed as "Sinsaenum II". It was later announced in summer that year that the band would release a new EP. The EP, entitled Ashes, was scheduled for release on November 10, featuring new music, previously Japan exclusive bonus tracks, and an alternate mix of the track "Dead Souls" from Echoes of the Tortured, remixed by Frédéric Duquesne of French industrial metal group Mass Hysteria. The title track was released with a music video on 29 September 2017.On October 27, they released the Duquesne mix of "Dead Souls" with a lyric video.