Karlsson was born in Katrineholm, Sweden where his father Björn was a greenkeeper at the local golf club.

His family lived close to the golf course, just next to the practice green, where Karlsson spent a lot of time.

[3] The month before, Karlsson represented Sweden at the European Amateur Team Championship, at Royal Portcawl, Wales, and finished tied fourth individually with Peter McEvoy, England, in the stroke-play qualification competition.

In 1999 he was eleventh on the Ryder Cup qualifying table just missing out on the last automatic place, and was not selected as a captain's pick.

He played again in 2008, forming a partnership with Pádraig Harrington in the foursomes and beating Justin Leonard 5 & 3 in the singles on Sunday.

After a strong finish to the season, Karlsson won the 2008 European Tour Order of Merit, being the first Swedish golfer to do so.

After the 2008 season, he also received the Swedish Golfer of the Year award, male and female, for the first time of two during his career.

He returned for The Vivendi Trophy toward the end of the season, and completed his recovery by claiming his tenth Tour title at the 2010 Commercialbank Qatar Masters the following January.

Like many leading Swedish golfers he lives outside his home country, formerly based himself in Monaco and in 2010 moved to Charlotte, North Carolina, United States.