He began his career at Þór Akureyri, and played one match for Dutch club AZ before joining England's Coventry City in 2008.

Aron plays for Iceland at international level, having made his senior debut in 2008, and has earned over 100 caps for the national team.

[10] At the end of his first season in England, Aron was voted the Coventry City Supporter's Player of the Year as well as the club's Community Award.

[18] However a deal for a new contract could not be reached between his agent and Coventry, and at the end of the season the club gave him a deadline date to agree to stay.

[20] On 8 July 2011, Aron agreed a three-year deal with fellow Championship team Cardiff City on a free transfer, as the fifth signing for new manager Malky Mackay.

[28] Following his return from Euro 2016, Aron was linked with a move away from the Welsh capital, with Derby County and Norwich City claimed to be interested.

[32] Aron returned to the side for the final run-in, where he scored the winning goal against Nottingham Forest and ultimately helped Cardiff gain promotion to the Premier League.

[34][35] In March 2019, it was announced that Aron would leave Cardiff at the end of the season, and would join Qatar Stars League club Al-Arabi.

Aron was named as the permanent captain of the national team before a friendly match against the Faroe Islands in August 2012 at the young age of 23, ahead of his 29th cap.

[44] Under his captaincy, Iceland qualified for the play-off round of FIFA World Cup qualification for the first time,[45] where they lost 2–0 on aggregate to Croatia.

[46] On 10 October 2014, Aron scored his first senior international goal in Iceland's 3–0 away win against Latvia in UEFA Euro 2016 qualifying.

[48] On 6 September, he was sent off in the last minute of a goalless draw at Laugardalsvöllur in Reykjavík against Kazakhstan, a result which put Iceland into their first major international tournament.

After their first match, a shock 1–1 draw with Portugal in Saint-Étienne, opposing skipper Cristiano Ronaldo accepted to trade shirts with him in the dressing room.