Career
Born in Trollhättan, Västra Götaland, Karlsson started to play table tennis in his hometown club at the age of 8. He remained in Trollhättan until he was 16, subsequently he moved away from home to go to high school. During his high school years Karlsson had 10 training sessions a week.
In 2011 he signed to Halmstad BTK and began to rose through the ranks quickly.
Ranked outside the top 400 in October 2010, Karlsson finished 2011 in the 233th position, and at the end of 2012 he ranked 129. The year 2012 also marked his first senior success, winning the silver medal at the 2012 Table Tennis European Championships in doubles.
His performances also attracted French top division side AS Pontoise-Cergy TT and Karlsson eventually signed to the club in September 2013.