Örn Arnarson has participated in three Olympics in 2000, 2004, and 2008. He is the first Icelandic male swimmer ever to participate in the finals for the Olympics back in 2000 when he came 4th place in the 200m backstroke.
In late 2008, Örn Arnarson moved to Denmark, where he became the Elite Coach at Aalborg Svømmeklub Elitehold. After working for other swimming clubs in Denmark, Örn Arnarson moved to the west coast to work at Esbjerg Svømmeklub. In 2017, Örn Arnarson received the award for Årets Årgangs Juniortræner at Dansk Svømme Award 2017.
In December 2016, Örn Arnarson got engaged to Vinni Bay.