Pregasina was first mentioned in documents in 1424. The area was probably already used as a place of refuge during the migration period and was subsequently inhabited by shepherds in the summer who grazed their animals here. Parts of the name are of Lombard origin, "gasina" means something like beautiful panorama, while "pre" refers to the pasture area (from the Italian prato = meadow, lawn). The first permanent settlers were charcoal burners and in 1633 the church dedicated to Saint George was built.
During the Risorgimento and the attempt by Italian irregulars to advance towards Trento, the town was briefly occupied by Italian troops in 1848 and again in 1866 after the Battle of Bezzecca, and was liberated from the insurgents by the Kaiserjäger, according to the wording at the time. By 1850, the municipality of Pregasina (Germanized as Pregasen) had 119 inhabitants and 41 houses.
With the outbreak of the First World War, the able-bodied male population was drafted at the beginning of August 1914. Women, children and the elderly remained behind. With the Italian declaration of war on May 23, 1915, they too were evacuated by the Austro-Hungarian authorities, after the population had only learned of the impending evacuation 12 hours earlier, on the afternoon of May 22. With the permitted luggage of 10 to 15 kilograms, they walked down the Ponale road to Riva on 23 May and boarded the train to Mori in the afternoon. Only the priest, the mayor and four other men remained in Pregasina to look after the remaining livestock. In Mori they had to wait three days until another train took them to Innsbruck. Most of Pregasina's inhabitants spent the war years in Bohemia, in Protivín, Pilsen and Budweis. Twelve of them died in the diaspora imposed by the war.
The first Italian patrols appeared in the town in July 1915. But it was not until 17 October of the same year that the Italian army report was able to report the capture of Pregasina, despite heavy artillery fire by the enemy, including gas grenades.
The Italian troops, in particular Alpini of the Vestone battalion, subsequently relieved by several companies of the Guardia di Finanza, also occupied the surrounding mountains, such as the Nodice (859 m above sea level), which had already been fortified by the Austro-Hungarian troops between 1914 and 1915, and the ridge between Cima Bal (1260 m above sea level) and Cima Nara (1376 m above sea level), partly converting them into fortresses. Two cable cars were also built to transport building materials obtained from the houses of Pregasina to the positions.
During the war, the town was shelled by artillery from both sides and was badly damaged. When the inhabitants of Pregasina were able to return to their village in 1919, they found the place almost completely looted and destroyed. The municipal administration went to great lengths, and with budget constraints, to work to make the houses habitable again and to repair the infrastructure, such as the municipal water supply and the roads and paths. The numerous fallen soldiers buried in the village cemetery also had to be exhumed and buried elsewhere.
With the Treaty of Saint-Germain, Pregasina was officially incorporated into the Kingdom of Italy, but retained the municipal statute drawn up under the Austro-Hungarian era, which was only abolished when the Italian municipal code came into force on 11 January 1923 in the new provinces that had become part of Italy after 1918. Even under Italian law, little changed in the municipality's financial difficulties. On April 13, 1924, the last mayor of Pregasina, Guido Toniatti, resigned along with the municipal council because they had not received any financial support from the Italian state and the request to join another municipality had not been heard. On July 23, 1925, Pregasina was finally incorporated into the municipality of Biacesa and thus ceased to exist as an independent municipality.
In 1929, Pregasina was connected to the electricity network and water supply. In 1955, Molina di Ledro, into which Biacesa had been incorporated in 1928, was connected to Riva del Garda.