His father, Count Giovanni Tosti, descended from an ancient Calabrian family, died young, and so his mother, Vittoria Corigliano, entrusted the child to his uncle, a monk at Monte Cassino.

Pius IX intervened personally to secure the liberation of the imprisoned Tosti, who, as Cardinal Alfonso Capecelatro relates, had been accused of belonging to a band of murderous conspirators.

He was sad to see convents threatened by a law of expropriation passed by the Parliament of the new Italian Kingdom and appealed to distinguished friends, such as the British statesman, William Gladstone, to obtain some exemption for Monte Cassino, which he likewise procured later for the Abbey of Grottaferrata, the Sacro Speco of Subiaco, etc.

This pope's allocution in May, 1887, inviting the Italian Government to make peace, presided over by the former revolutionary, Francesco Crispi, rekindled Tosti's patriotism.

Crispi's impatience, mutual opposition, and the distrusts of French diplomats, thwarted his efforts, and he had to retract publicly his brochure La conciliazione.