In his youth he was one of the founders of the Green Cross of Adria and graduated in Law at the University of Padua, where he became part of an irredentist group called "San Giusto Battalion".

Of republican ideas, he frequented the socialist-republican circles in Adria for some time, together with Giovanni Marinelli, but after attending a rally held by Benito Mussolini while finding himself by chance in Milan, he joined the Italian Fasces of Combat in April 1921.

This led to negotiations between state and church that in October 1936 resulted in the resignation of Fogar, who was transferred to Rome, where he was appointed titular archbishop of the Archdiocese of Patras and assigned to the basilica of San Giovanni in Laterano.

He resigned for health reasons after two months, after which he was placed at the disposal of the Ministry of Finance, with the post of Commissioner for Paper and Cellulose and then of President of the National Institute for Consumption Tax Management.

In the days that preceded the collapse of the Italian Social Republic, Tiengo was present at the meeting hosted by Cardinal Ildefonso Schuster in the archbishopric in Milan in the morning of 25 April 1945 between Mussolini and the leaders of the local Committee for National Liberation in a final attempt to persuade the Duce to surrender.