He completed postgraduate studies in systematic theology and the philosophy of religion at the University of Bonn in West Germany from 1958 to 1966.

He wrote his thesis on the concept that the Orthodox Church possessed infallibility when it acted together in conciliarity (e.g. the Ecumenical Councils).

In 1965, whilst still completing his postgraduate studies, Harkianakis was appointed Professor of Theology at the University of Athens.

In 1970, Harkianakis was elected the Titular Metropolitan of Militoupolis (whilst remaining in the Holy Monastery of Vlatadon) as exarch in matters concerning Northern Greece and Mount Athos.

Harkianakis died following a lengthy illness in Sydney on 25 March 2019, on the Holy Day of the Annunciation of the Theotokos.