On October 22, 1866, the populations of Veneto and Mantua participated in a plebiscite to ratify their recent annexation to the Kingdom of Italy. This annexation had occurred three days prior, culminating a series of military and political efforts during the Third Italian War of Independence against the Austrian Empire. The plebiscite was a vital step in the broader movement towards Italian unification, known as the Risorgimento. The desire for national identity and self-determination heavily influenced the votes in these regions, traditionally attributed to a longstanding history of foreign rule and local autonomy.

The plebiscite reported an overwhelming majority in favor of joining Italy, further solidifying the notion of a unified Italian state. The decision reflected the prevailing nationalist fervor among the citizens in Veneto and Mantua, fueled by Italian national leaders like Giuseppe Garibaldi and Count Camillo di Cavour. As a means to legitimize the annexation, the plebiscite was also an effort to showcase democratic principles and popular consent.

Following the ratification, the incorporation of these territories into Italy marked a significant milestone in the nation's unification process. Veneto's history as part of the Republic of Venice and Mantua’s historical significance added to the cultural and political fabric of the newly consolidated Italian state. This event not only reshaped the geopolitical landscape of Italy but also contributed to the larger narrative of nationalism in Europe during the 19th century.