His feelings as a patriot and his love for pseudo-classicism led him to associate himself with the coterie about the poet Manuel José Quintana, and to imitate the latter's metres.

With intensified liberal tendencies, Gallego presented himself for election and was returned a deputy to the Cortes Generales.

He had consistently opposed Napoleon's invasion of Spain, with both pen and voice, yet the despotic Ferdinand VII, after his return in 1814, imprisoned him because of his liberalism.

The most famous of the few compositions left by Gallego is the elegy El Dos de Mayo, which commemorates the events of the patriotic uprising of 2 May 1808, by a few hundred Spanish civilians and militarymen, including the artillery captains Daoiz and Velarde, and infantry lieutenant Ruiz.

Gallego's words, urging his countrymen to resist unto death, are said to have had a major effect.