[1] After finishing primary school, Franc graduated a Minor Seminary in Vipava with the secondary education during 1974–1978 and also served his compulsory military service in the Yugoslavian Army.

Here he continued his seminary formation in the Collegium Germanicum et Hungaricum and completed his studies with a Doctor of Theology degree in Fundamental theology at the Pontifical Gregorian University[2] and was ordained as priest on June 29, 1985, for his native Archdiocese of Ljubljana.

Šuštar was engaged in pastoral work and served as priest in Ljubljana-Moste and Ljubljana-Fužine parishes from 1985 until 1991.

For two years, Archbishop Alojz Uran appointed him cathedral pastor in Ljubljana and archdeacon.

After two years, in 2007 he was re-appointed director of the Major Theological Seminary in Ljubljana and a canon of the cathedral chapter.