In 2005, Karlsson made his debut as a playwright with the play Nattpromenad (Nocturnal Walk) for the Stockholm City Theater, which received rave reviews from audience and critics alike. Spurred by the joy of writing for the stage, Karlsson began writing fiction, which resulted in his debut as a writer: the twisted, humorous and intelligent short story collection Det andra målet (The Second Goal). With an actor's ear for the pauses that endow dialogue with meaning and a singular ability to register moods and emotions, Karlsson displays a Carver-like capacity for placing his short stories in relation to each other, so that the whole becomes something beyond the sum of its parts.