Shellback initially started his career as a heavy metal guitarist before transitioning into pop music production and songwriting.

Shellback regularly collaborates with songwriter Max Martin and together they have produced, written, or co-written songs for various artists such as P!nk, Taylor Swift, Adam Lambert, Britney Spears, Usher, Avril Lavigne, Ariana Grande, Adele and Maroon 5.

along with Martin and Justin Timberlake for the animated film Trolls (2016), earning a nomination for the Academy Award for Best Original Song in 2017.

[citation needed] He started as a drummer in local indie rock bands in Karlshamn, as well as recording all instruments on the 2003 Meriah demo ...Turn Him Your Other Cheek (a strictly black metal recording), before joining the hardcore-metal scene as a vocalist in 2004 for Blinded Colony, with whom he recorded 2005's Promo Demo and 2006's Bedtime Prayers, drawing comparisons to fellow Swedish melodic death metal band In Flames, before leaving in 2007.

[citation needed] In 2005, he also performed as a guest musician on the Faith album Sorg.