Karlsson was selected in the third round, 87th overall, of the 2018 NHL Entry Draft by the San Jose Sharks.
[2][3] On 25 February 2019, his NHL rights were traded to the Vancouver Canucks in exchange for Jonathan Dahlén.
On 27 May 2022, Karlsson was signed to a two-year, entry-level contract with the Vancouver Canucks.
[5] He made his NHL debut on November 16, 2023, in a 5–2 loss to the Calgary Flames, recording three shots in 11:54 of ice time.
This biographical article relating to a Swedish ice hockey centre is a stub.