[4] In his first professional season, Arnason started out with the Blackhawks but due to poor conditioning spent most of the year with the team's American Hockey League (AHL) affiliate, the Norfolk Admirals.

[4] During the season, Arnason recorded his first career NHL hat trick, scoring all three Chicago goals in a 3–3 tie versus the San Jose Sharks on December 28.

[11] With the Blackhawks that season, Arnason had tallied 13 goals and 41 points in 60 games[12] when, on March 9, 2006, he was traded to the Ottawa Senators in exchange for Brandon Bochenski and a second-round pick in the 2006 NHL Entry Draft.

[18] On September 17, 2009, Arnason failed to make the Rangers out of training camp and was assigned to their AHL affiliate, the Hartford Wolf Pack, for the beginning of the season.

[19] On November 10, 2009, without the ambition to play in the AHL he was suspended by the Rangers and released from his contract to sign with the European team Dinamo Riga of the Kontinental Hockey League.

[21] Returning to North America, as a free agent, he accepted a tryout invitation to attend the Florida Panthers training camp for the 2010–11 season.

[22] Subsequently, released from the Panthers during the preseason, Arnason then initially accepted another invite to his local AHL club, the Manitoba Moose, affiliate of the Vancouver Canucks, before electing to not report to camp on September 27, 2010.

[23][24] Arnason then accepted a temporary contract to return to Europe, signing with Swiss team EHC Biel of the National League A (NLA) on October 14, 2010.

[25] He scored 10 points in 9 games with Biel before he moved on to EHC Visp of the National League B (NLB), signing a contract for the remainder of the season on November 11, 2010.

[26] However, a week later, Arnason was released playing in just a single game with Visp, after both parties mutually opted to exercise an exit clause in the contract on November 18, 2010.