The highly-rated Swede cost the Black Cats £1.5 million when he signed from Goteborg last summer.
Karlsson, 19, has played 11 games for the Swedish under-19 side.
Karlsson is Killie’s third signing of the January window, alongside cult hero Alexei Eremenko and West Brom loanee Vitalijs Maksimenko.
Kilmarnock have also announced the departures of David Silva and Caoimhin Bonner. The duo left Rugby Park by mutual consent.