The territory covered is that of the Swiss canton of Ticino, where the population is almost entirely Catholic and Italian is the common language.

Before the Diocese of Lugano was founded, the Canton of Ticino was under the jurisdiction, in ecclesiastical matters, of bishops who were not Swiss.

Soon after the formation of the Canton of Ticino, in 1803, efforts were made to separate it in its church relations as well as from foreign powers and to unite it in these with the rest of Switzerland.

Without consultation with the Holy See, the Federal Council in 1859 declared the jurisdiction of the Bishops of Como and Milan to be abolished in the territory of Switzerland; after this negotiations were begun with Rome.

The most noted church of the diocese is the Cathedral of San Lorenzo at Lugano, which was built in the fifteenth and sixteenth centuries and has a celebrated Renaissance façade; the most frequented place of pilgrimage is the shrine of the Madonna del Sasso not far from Locarno, which is the national shrine of the Canton of Ticino.