Born in La Paz, Bolivia and a career military officer, Belzu participated in a number of conspiracies and rebellions, which were frequent during the turbulent first 50 years of Bolivian independence. He rose to the position of commander of the Army during the early years of the José Ballivián presidency (1841-47). Originally a supporter of Ballivián, Belzu turned against him when Ballivián had apparently attempted to seduce his wife. Undoubtedly political ambitions -- typical of upper-level Bolivian military officers at the time -- also played a key role in the general's decision to do whatever he could to topple Ballivián from that point on. Indeed, sworn to undying enmity, Belzu never ceased to conspire against the president. By 1847, his forces controlled a large portion of the Bolivian countryside and were moving against the de-facto seat of government, La Paz. At this point Ballivián fled to exile abroad, leaving the government in the hands of general Eusebio Guilarte, head of the Council of State and, legally, second-in-line to the presidency. Guilarte could not hold off Belzu's hordes, and within weeks abandoned the palace as well. A counter-coup by general José Miguel de Velasco had to be put down, but within weeks Belzu was installed as de fact president of Bolivia.
Belzu soon a decidedly populist inclination, one perhaps stemming from his personal enmity against the patrician former president José Ballivián. Indeed, Belzu proclaimed himself to be a hater of the upper classes, and at least in rhetoric, extolled the virtues of the long-neglected Bolivian majorities (known in the country as Indians), who dubbed him "Tata" (colloquial for father). He tried to fashion a more egalitarian sort of government, but this clashed with his desire to maintain firm control. Most of Belzu's reforms were merely cosmetic, although his discourse seems to have ben far more liberalizing than any president's had been seen since Sucre. Despite having called a hand-picked "Congress of notables" to rubber-stamp or legitimize his rule, he nonetheless faced constant opposition and rebellions from the "constitutionalist" pro-Ballivian camp, from ambitious fellow military warlords, and later, from pro-Linares factions.
Following a prolonged, 7-year dictatorship, in 1855 Belzu decided to "retire" and ran elections in which he sponsored the candidacy of his loyal son-in-law, general Jorge Córdova. The latter was duly elected, and for two years ruled Bolivia as a virtual proxy of the powerful former president. During this time, Belzu served as a Bolivian diplomat in Europe. Córdova, however, was overthrown in an 1857 coup d'état, and Belzu soon returned to Bolivia with renewed hopes of returning to the presidency. He conspired for years, and was on the verge of attaining power when he was assassinated in 1865, presumably at the hands of the new dictator Mariano Melgarejo.