Zilliacus went to the Zilliacuska skolan, the Swedish-language, private, co-educational school established by his grandfather's uncle Laurin Zilliacus. Upon graduating, in 1972, Zilliacus enrolled at the University of Helsinki, where he was the editor-in-chief of the national student paper Studentbladet and three times elected as chairman of the Student Union, as well as at the Hanken School of Economics. As a promising young football player, he took time off from his studies for one term to spend one season in the youth academy of Fluminense in Rio de Janeiro.
