Harrison regularly writes articles for the Swedish journal Populär Historia (Popular History).

Harrison regularly gives lectures to the general public on a broad range of historical topics.

Harrison is the editor-in-chief of a comprehensive series about Swedish history published by Norstedts with the first volume released in September, 2009.

The Swedish TV channel TV4 has made a companion television series for which Harrison is the historical consultant and co-host along with Martin Timell.

Harrison was born in Huddinge, Stockholm County, and spent much of his youth in Staffanstorp in Scania.