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As a child he was ungovernable, as those proved to be whom he freed from 300 years of Spanish rule. Born to a family of randy Venezuelan aristocrats, he spent a formative period in Europe. In Paris, the scientist Alexander von Humboldt planted in Bolívar the germ of a political idea – that one man could change the course of history; in Italy, such a man, Napoleon, even trained his telescope on him (perhaps thinking Bolívar was a spy). In Madrid, Bolívar played an irascible game of shuttlecock with the future King Ferdinand VII, and witnessed the lecherous Spanish queen, disguised as a monk, visit her lover in the room next door. And in Rome, after refusing to kiss the feet of the Pope, Bolívar vowed on his knees to expel the Spanish from his country.

Populations were cut in half in the ensuing violence between the patriot and royalist forces. The number of beheadings, of babies squirming on lances, of butchering maniacs like Bolívar's epileptic General Páez ("he would become so excited by the carnage that he would foam at the mouth and topple from his horse") makes Cormac McCarthy's Blood Meridian seem, by contrast, a picture of languorous bonhomie. Arana writes: "There is a reason why blood trickles down roads and heads roll out from under bushes in Latin American literature: this is not magical realism. It is history. It is true."

I suspect that one reason why her biography is so plausible and engagingly told is that the Peruvian-born Arana is herself a writer of fiction. Like García Márquez (who memorably fictionalised Bolívar in The General in his Labyrinth), she has an instinct for the vitalising detail – the bleached bull's skull that Bolívar used as a chair; the pots and pans of Indian women known as rabonas clanging as they hurried after Bolívar's army over that inhospitable terrain. As well, his sad and contradictory story demands a novelist's empathy.

He was an unsated womaniser. When he triumphantly entered Caracas in 1813, he was borne, like Caesar, in a chariot drawn by daughters of the most prominent families. Many of the girls who placed a wreath on his head became mistresses, loving him fiercely through thick and thin. His conquests included 18-year-old Manuelita Madroño, who eschewed all other men until she died aged 92. Up until the last, villagers would ask: "So how is Bolívar's old lady?" And her reply: "As fresh as a little girl."

His men were much fickler. Bolívar's revolutionary theory was: attack and unite. The second seemed harder to achieve. US president John Adams believed: "You might as well talk about establishing democracies among the birds, beasts, and fishes as among the Spanish American people." And so it proved. Near the start of his liberation campaign, Bolívar had announced that "regular elections are essential to popular government". His vision was for a federation of republics. But the French and North American model did not suit a continent of mixed races who required their own laws. Freedom from Spain only spawned distrust, and vicious and ruinous intrigue. Seven years later, the social realities of the continent had altered his vision. From now on, declared Bolívar, "we shall avoid elections, which always result in… anarchy".

In Bolivia, named after him, two of out the three presidents who came to power over a span of two days were murdered. "Everywhere I look, I see only misery and distrust… a dictatorship will solve everything." Never having aspired to government, the man who had warned that the nation in which one man ruled was a nation of slaves, warily assumed power.

As with San Martín, liberator of the south, it all ended badly. Caught between rebels and assassins, Bolívar spent his years in power dodging conspiracy after conspiracy. In one of his last proclamations, he itemised what two decades of rule had taught him. "1. America is ungovernable; 2. He who serves a revolution ploughs the sea; 3. All one can do in America is leave it."

In exile, Bolívar was hoping to live – like San Martín – in London, where his agent López Méndez had recruited 5,300 British troops to serve in corps like the 1st Venezuelan Hussars. Bolívar preferred the English system of government to the North American, and nurtured ideas that his longed-for federation would become a protectorate of England. That being so, it is disappointing that the English publisher of this newest and best biography of him should give us an edition with North American spellings. At the risk of sounding like President Hollande, why bother to have a separate English edition at all unless to cherish and safeguard the distinctions between our two languages? As Bolívar reminds us: "Doing the right thing costs so little and is worth so much."

Bolívar: the Epic Life of the Man Who Liberated South America by Maria Arana

624pp, W & N, t £23 (PLUS £1.35 p&p) 0844 871 1515 (RRP £25)

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