Karlsson, 19, has registered 17 points (4-13-17) in 48 games for Karlskrona HK in the Allsvenskan. In 2017.18, Karlsson registered 27 goals and 25 assists (27-25-52) in 42 games for Karlskrona Junior in the SuperElit league. He tied for the league lead in goals and finished tied for second in points en route to being named the league's top player.
A native of Eksjo, Sweden, Karlsson represented Sweden at the 2019 World Junior Championship collecting an assist in three games.
The 6-1, 187-pound forward was selected by San Jose in the third round, 87th overall, at the 2018 NHL Entry Draft.