Bjørnson has released sixteen studio albums with Enslaved and won five Norwegian Spellemann Awards with the band.

He is, along with Grutle Kjellson, one of only two founding members left in the current line-up of Enslaved, having been only 13 years old at the time of the band's formation in 1991.

[3][4] After Phobia's split, the two formed Enslaved as a band more in the vein of the black metal style and with their shared fascination with Norse mythology as a foundation.

[6] He stated that "When we started Enslaved we wanted to have the same level of commitment to something spiritual as our contemporaries in black metal [have with] the Satanic side.

[11] The arrangement was titled 'Skuggsjá', and was performed by Enslaved and Wardruna as a concert piece at the Eidsivablot festival in Eidsvoll, Norway, on 13 September 2014.