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.
Coventry were due compensation via him being under the age of 24.

He made his debut on 7 August in the first match of the new season, playing the full 90 minutes in the 1–0 away win over West Ham United.
In his second match, Aron limped off with an ankle injury after only ten minutes against Bristol City, the injury sidelining him for a week.
He returned after the September international break, insisting his injury was behind him.
On 22 October, Aron scored two goals in a 5–3 victory against Barnsley, receiving the man of the match award.

Aron played the entirety of the 2012 Football League Cup Final, as City were beaten 3–2 on penalties after by Premier League club Liverpool at Wembley Stadium.

Aron scored Cardiff's first goal in the Premier League on 25 August 2013, against Manchester City in a 3–2 win.
In June 2015 he signed a new contract with the club, until the summer of 2018.

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.
However, Cardiff City manager, Paul Trollope, described him as "a very important player" to the club.
His performances under Trollope and his eventual replacement Neil Warnock saw him awarded the club's Player of the Year award at the end of the season.

The following season, Aron failed to nail down a consistent place in the starting eleven, due to a number of injuries throughout the first half of the season.
Despite his injury problems, Cardiff offered him a new contract, which was later rejected by the player.
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.

In July 2018, Aron signed a new one-year deal.

In March 2019 it was announced that Aron would leave the club at the end of the season, and would join Qatari club Al-Arabi.
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. Coventry were due compensation via him being under the age of 24.
He made his debut on 7 August in the first match of the new season, playing the full 90 minutes in the 1–0 away win over West Ham United. In his second match, Aron limped off with an ankle injury after only ten minutes against Bristol City, the injury sidelining him for a week. He returned after the September international break, insisting his injury was behind him. On 22 October, Aron scored two goals in a 5–3 victory against Barnsley, receiving the man of the match award.
Aron played the entirety of the 2012 Football League Cup Final, as City were beaten 3–2 on penalties after by Premier League club Liverpool at Wembley Stadium.
Aron scored Cardiff's first goal in the Premier League on 25 August 2013, against Manchester City in a 3–2 win. In June 2015 he signed a new contract with the club, until the summer of 2018.
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. However, Cardiff City manager, Paul Trollope, described him as "a very important player" to the club. His performances under Trollope and his eventual replacement Neil Warnock saw him awarded the club's Player of the Year award at the end of the season.
The following season, Aron failed to nail down a consistent place in the starting eleven, due to a number of injuries throughout the first half of the season. Despite his injury problems, Cardiff offered him a new contract, which was later rejected by the player. 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.
In July 2018, Aron signed a new one-year deal.
In March 2019 it was announced that Aron would leave the club at the end of the season, and would join Qatari club Al-Arabi.
Aron Gunnarsson