He turned professional in 2006. He topped the
Nordic League rankings in 2007 to earn a tour card on the
Challenge Tour. His best finish on the Challenge Tour was T4 at the 2008
Reale Challenge de España. Karlberg earned his 2010
Asian Tour card through
qualifying school. He won the second Asian Tour event he played, the
SAIL Open. Later in the year, he won his second Asian Tour title at the
Hero Honda Indian Open. Karlberg earned a 2015
European Tour card through
qualifying school, and won the
Open d'Italia during his rookie season, after holing a birdie putt on the second extra hole in a play-off against
Martin Kaymer. He finished runner-up at the
2016 BMW PGA Championship en route to a career-best 69th a month later on the Official World Golf Ranking and a season finish of 34th in the
Race to Dubai. After battling illness which forced him to step away from competitive golf, he holed a 50-foot birdie putt on the final hole of
2019 Qualifying School to earn the final European Tour card for 2020. At the 2021
Dubai Duty Free Irish Open in early July, Karlberg finished runner-up, after holing a chip from the greenside rough on the 72nd hole. The achievement earned him €314,170 in prize money and a late spot at
The 149th Open Championship two weeks later. ==Professional wins (8)==