The band was founded in the beginning of 1990’s by Dariusz “Profesor” Kudelski and Tomasz “Choina” Choiński. Susequently other members joined the band: frontman Marcin “Brazyl” Jastrzębski, guitarist Zbigniew “Łysy” Klifert and drummer Adam “Żurek” Żuromski (known later also from Christ Agony and Ash Devili bands). That was the first lineup of Insidius. The band was active on Olsztyn metal scene for two years. After that the activity was suspended.
After nineteen years Insidius was reactivated in the following lineup: Choina (guitars), Profesor (guitars), Brazyl (bass/vocals) and Żurek (drums). The members started working on new material. In 2012 Mori joined the band replacing Profesor as a guitarist, who took over the bass in stead of Brazyl, who had left Insidius earlier. In 2013 Rafał “Tasio” Tasak (ex-Prophecy) joined the band as a vocalist. In this refreshed lineup Insidius continued work on their debut album. The band played series of gigs (Festiwal Wspomnień im. Szymona Czecha, Olsztyńska Ofensywa 2013, 30th anniversary of Vader, Metalowa Wigilia 2013) which allowed them to present their music in front of wide audience.
In 2014 the band was busy with production of their debut album. They also played several gigs in the meantime. In that year the replacement of drummer took place. Żurek left the band and Michał Andrzejczyk (Deithwen) took over his position.
Insidius played on the following events: Festiwal im. Szymona Czecha, Covan Wake Up For Us, Grill’n’Grind and Sun Dies Festival #2. In fall the band entered Hertz Studio with complete album material. Not only drum tracks were recorded but also mix and mastering were done by Hertz.
The first single “The Final Journey”, promoting the “Shadows Of Humanity” album, was published. Music video was made for the song by Exploited Media. Official release date of the “Shadows Of Humanity” was on 29th April 2016. The album was released independently.
Songs from “Shadows Of Humanity” were played live on following events: In Your Face #3, Thrash Attack #15, Death is Coming to Your Town, Imperium Poloniae 2016. By the end of the year the band went back to rehearsal room to start working on their second album.
Mori left the band and was replaced by musician from Olsztyn – Lasota (Varmia). work on the second album was continued until the end of the year.
Insidius entered Hertz Studio for the second time in order to record new material. The work was finished by the end of July.
In March one of the band’s founders – Profesor – left and was replaced by Łukasz “Jankes” Usydus (Soul Skeleton) on bass. A change in guitar section also occured: Jakub “Janus” Janowicz (Northern Plague) took the place of Lasota.
The promotion of the second album began on the “XXXV years of Chaos” tour where Insidius was honored to perform along famous metal bands: Vader, Marduk and Arkona. The tour covered nine Polish cities.