His clubs include Real Betis, Aston Villa, Wolverhampton Wanderers, Leicester City, AZ and Burnley.
Jóhannes Karl began his professional career in the Icelandic Premier Division with KA of Akureyri at the age of 17.
In 2001, he moved to La Liga side Real Betis, his fourth new club in four years, signing for a fee of £500,000 from RKC Waalwijk.
Jóhannes Karl made his Wolves debut coming on as a substitute in their 0–0 league draw at home to Portsmouth on 30 August 2003.
[5] He made his Leicester debut coming on as a 73rd-minute substitute in their 2–1 away victory at Derby County on the opening day of the 2004–05 season.
Jóhannes Karl made 41 appearances in all for Leicester during his first season at the club, scoring four times in all with two of them coming in the league.
However, he struggled to establish himself in the AZ team, and quickly returned to English football in January 2007, just five months after joining the club.
He had been linked with a return to Leicester City, but this was in the middle of Milan Mandaric's takeover of the club so the Foxes could not sort out their finances in time.
He was then dropped from the squad entirely under Steve Cotterill after failing to impress but his fortunes changed when Owen Coyle took over as Burnley manager and he found himself back on the bench.
On 3 May 2009, Jóhannes Karl scored the fourth goal against Bristol City in a 4–0 win, which send Burnley to qualify via the Championship Play-offs.
In April 2010, he was suspended for two weeks by Burnley after comments he made to an Icelandic website where he questioned the team spirit under manager Brian Laws.
He joined the club on a two-year contract,[10] despite having offers from a higher division, stating the ambition of Town's management team and board persuaded him.
On 16 October, he scored his first goal for the club in a league match against Southampton at the Galpharm Stadium where Huddersfield won 2–0.
His second goal came in the 1–0 victory away at Charlton Athletic on 16 April 2011, he then went on to finish his first season with the club on 48 appearances in all with 38 coming in league and scoring twice during the 2010–11 campaign.
He made his first appearance of the campaign in the 2–0 home victory over Exeter City on 25 February 2012 in new manager Simon Grayson's first game in charge, coming on as a 63rd-minute substitute to a standing ovation.
On 27 April 2012, his contract at the club was terminated by mutual consent, citing "family reasons", and he returned to his native Iceland after making 56 appearances for the Terriers over two seasons scoring twice.
[13] Jóhannes Karl told the club website: "I would have liked to have played more during my two seasons, but that is football and you have to respect those decisions and the people who make them.
"[14] His release by the club saw Grayson express sadness to see Jóhannes Karl go due to his contribution to the side's efforts that season.
Jóhannes Karl made his international debut for the Iceland national team on 15 August 2001, in a 1–1 friendly draw with Poland.
Jóhannes Karl picked up his 16th and 17th caps for Iceland against England and Japan in a mini tournament held in Manchester prior to Euro 2004.
His father, Guðjón Þórðarson, has managed Stoke City, Notts County, Barnsley and the Iceland national team.