[1] He began his professional songwriting and production career in 1996 working at Cosmos Studios together with Kent (Gillström) Isaacs and Bloodshy.
In 1997, the founders of Murlyn Music, Anders Bagge and Christian Wåhlberg, saw the potential in Arnþór and Bloodshy, and handpicked them for the newly formed production company.
"[2] During his tenure at Murlyn Music (until 2003) a series of hits were created for artists such as Janet Jackson, Jessica Simpson, Ronan Keating, Jennifer Lopez, Samantha Mumba and Celine Dion.
In 2008 Arnþór founded the Swedish-based record and production company, Aristotracks, together with businessman Linus Andreen and artist Emilia de Poret.
On 7 September, Arnþór won Popjustice's 2011 Twenty Quid Music Prize for "Song of the Year" with "Higher" by The Saturdays.