Karlsson started out as his professional songwriting career under the alias of Bloodshy alongside his partner Pontus Winnberg, known as Avant.  They achieved their first success on Christina Milian’s debut album in 2001 and very quickly moved onto creating songs for pop acts like the Sugababes and legendary UK MC Ms Dynamite.  A defining moment of this era of Karlsson’s work was writing and producing Toxic for Britney Spears in 2005, which went on to win the Grammy for Best Dance Recording in 2005.

Karlsson then established the Miike Snow project in 2007, bringing alongside him US vocalist Andrew Wyatt and they released their debut album in 2009.  The band have also fully embraced remix culture both for themselves and for other artists.

Next, Karlsson began the Galantis project in 2013 with Linus Eklow using a remote studio in the Baltic Sea as their inspiration, releasing their first single Smile in November 2013. The group enjoyed especially good success with the single Runaway (U & I), which was nominated for Best Dance Recordings at the Grammys.  The debut Galantis album was released on the 8 June 2015.