Mameli was deeply involved in nationalist movements and some more "spectacular" actions are remembered, such as his exposition of the Tricolore (current Italian flag, then prohibited) to celebrate the expulsion of Austrians in 1846.

In March 1848, hearing of the insurrection in Milan, Mameli organised an expedition with 300 other patriots, joined Bixio's troops that were already on site, and entered the town.

Back in Genoa, he worked more on a literary side, wrote several hymns and other compositions, he became the director of the newspaper Diario del Popolo ("People's Daily"), and promoted a press campaign for a war against Austria.

In December 1848 Mameli reached Rome, where Pellegrino Rossi had been murdered, helping in the clandestine works for declaration (9 February 1849) of the Roman Republic.

Mameli soon left again for Rome, where the French had come to support the Papacy (Pope Pius IX had actually escaped from the town) and took active part in the combat.