Blom was born in Ekerö (Sweden) and is the brother of Anna Dunér. He studied humanities at the universities of Trier, Stockholm, Uppsala and Freiburg, where he became a member of Corps Suevia Freiburg. In 1996, he earned a degree in archival studies. He is one of the founders of the Verein Corpsstudenten in Schweden (Students' Club Corp in Sweden), a board member of the Concordia Catholica (the Catholic Union) and an active member, among other things, of the Sällskapet Emil Hildebrands Vänner (Society of Emil Hilde's Friends) and Par Bricole. He was previously vice president of the Katolsk historisk förening i Sverige (Catholic Historical Association in Sweden).