The young viscount of Matarrosa, the title he bore in his fathers' lifetime, was introduced to the writings of Voltaire and Rousseau by the abbot of the Benedictine house of Montserrat in Madrid.

He was present at Madrid when the city rose against the French occupation led by Marshal Murat on 2 May 1808, and took part in the struggle which was the beginning of the Peninsular War.

In the following year he was a leader of the party which compelled the Regency to summon the Cortes to which he was elected by Asturias early in 1811 though he was short several months of the legal age of twenty-five.

He was the more an object of suspicion because his brother-in-law, Juan Díaz Porlier, perished in a wild attempt to support the constitution by force.

His tenure of the premiership lasted only until September 14 of the same year, when the regent's attempt to retain a practically despotic government under a thin constitutional veil broke down.

Toreno is chiefly remembered as the author of the History of the Rising, War and Revolution of Spain, which he began between 1823 and 1832 and published in 1836–1838 in Paris.