[1][2][3][4] Karlsson came to prominence in 2018, when he won the silver medal at the Swedish Under 21 Championship.
He also helped Sweden reach the final of the 2018 Team Speedway Junior World Championship.
Karlsson also competed for Sweden in the finals of the 2018 and 2020 Team Junior European Championship.
[6] In 2022, for the third time he helped Sweden reach the final of the 2022 Team Speedway Junior European Championship, recording a fourth-place finish and also in 2022 he rode for Griparna in the Swedish Allsvenskan.
In 2023[7] and 2024, he signed for Västervik in the Swedish Eliserien (the highest league in Sweden).