In November 1889, just as the chugging compound engines of steam ships were beginning to take the wind out of the elegant sails of the great rake-masted clippers, an out-of-work Polish sea captain, unable to find a command in London, signed up with a Belgian shipping company.

A job had just turned up in Congo Free State, the private fiefdom of King Leopold II of Belgium – the previous occupant of the post had been killed in mysterious circumstances – and Captain Konrad Korzeniowski soon found himself setting sail down the African coast: “If only you had seen all the tin boxes and revolvers,” he wrote to a friend, “the high boots … and all the bottles of medicine.”

The imperial “Scramble for Africa” was just beginning, and the Belgians had laid claim to great chunks of central Africa. The venture which had started off as a nominally philanthropic attempt to stamp out the Arab slave trade and bring “progress” to the Congo, soon degenerated into a brutal land and power grab.

Rather than develop the Congo, the Belgians merely plundered it, attempting to export vast quantities of ivory and rubber to Brussels, at great profit, using forced labour. In the process the jungle was cut back, elephants were driven to the brink of extinction, villages were wiped out, the people who lived there compelled to perform hard labour, bound in chain gangs and whipped with rhino-hide chicottes – a regime that was in almost all ways more brutal than that of the Arabian slavers who preceded them.

By the time the captain turned up, the brutality, greed, violence and the hypocritically exploitative nature of the regime was in plain sight: on a march into the interior he saw innocent village boys bleeding from the wounds of Belgian gunshots, rotting bodies everywhere, and skeletons tied to posts. Soon he came to loathe his Belgian colleagues who had come, he wrote, “to tear treasure out of the bowels of the land… with no more moral purpose… than a burglar breaking into a safe”.

Captain Korzeniowski meant to stay three years in the Congo, but after just five months of navigating the great waterways between Kinshasha and Kisangani, he resigned, chronically ill and an emotional wreck. He retired to Switzerland “in a state of psychological and moral despair” convinced of “the universal potential for savagery, and the hollowness of civilisation”. He only narrowly avoided a nervous breakdown. But he brought back more from the expedition than dysentery and depression. The notes and jottings the captain had made on his journey infiltrated their way first into the manuscript of a novel named Almayer’s Folly that he worked on upriver to keep himself from boredom and madness; then into a short story called An Outpost of Progress; and finally, in 1899, into what would become his most famous novel, Heart of Darkness.

Joseph Conrad – the name the captain assumed when he took British citizenship – has been well served by biographers and critics; but it is hard to imagine any student of his work will produce a more strikingly original book than Maya Jasanoff’s magnificent The Dawn Watch. It is not quite a biography or a work of criticism, though it contains elements of both, and fragments of travel writing too. It is instead both a circumnavigation of Conrad’s world and a profound meditation on globalisation and colonialism, and of Conrad’s place in forming our perceptions of both. It takes us from Poland, through Marseille and London then around south-east Asia until the book’s climax, when we travel up the Congo in Conrad’s footsteps, and Captain Korzeniowski turns his hand to writing – initially, somewhat surprisingly, “when he saw that the magazine Tit-Bits ran a competition for stories by sailors”.

Jasanoff writes beautifully and the book is worth reading alone for her finely crafted descriptions of 19th-century Singapore, Marseilles and London, as well as her mastery of seadog slang. But The Dawn Watch is far more than the sum of its parts. Jasanoff shows how Conrad was one of the first writers to grapple with the great issues of our time: terrorism, immigration, globalisation, and “the way power operates across continents and races”. Conrad’s world, she writes, “shimmers beneath the surface of our own”.

Most writers’ biographies tend to start slowly and only pick up pace in adulthood; but this is not the case with The Dawn Watch. The opening section, dealing with Conrad’s Polish childhood, tilts us straight into the world of 19th-century revolutionaries that Conrad depicted so memorably in Under Western Eyes, and gives Jasanoff some of her best material.

Conrad’s father was a leading Polish poet, nationalist thinker and agitator who dreamed of freeing his country from the yoke of tsarist Russia. His activities led to his movements being monitored by the Russian secret police and eventually, when Conrad was three and half years old, Apollo Korzeniowski was “disappeared” into Pavillion X, “an immense dungeon where Tzardom buries Polish patriotism” in the Warsaw Citadel. There, after several months with no official acknowledgment of his detention, Apollo and his family were sentenced by military tribunal to internal exile on the edge of Siberia where both parents quickly fell sick and in 1869 the 12-year-old Conrad found himself an orphan. From here we follow him to Kraków, Marseille and then to London which he found much more to this taste. It was here, much later in life, that he would set one of his finest novels, The Secret Agent, but in a London that owed as much to Conrad’s memories of the revolutionary underground of his childhood as it did to the Victorian city imagined into fictional life by Conrad’s great literary hero, Dickens.

It was also in London where Conrad’s first career as a sailor really took off. Before long he was heading to Java, Borneo and the Malay straits, picking up the ways and the language of the sea which would fill all his early novels, culminating in Lord Jim.

The final phase of his life took him via the horrors of the Congo and the success of the writing which that inspired, to a very different life as an author settled in the unlikely soil of rural Kent and a member of the brotherhood of Victorian novelists, firstly through his country neighbours, Henry James and HG Wells, and later through the two men who would become his adoring Boswells, Ford Maddox Ford and a young Scottish critic called Richard Curle who published the first book-length analysis of Conrad’s work and declared him to be “one of the greatest, least appreciated, and most misunderstood writers alive”.

The wide range of experiences that Conrad lived through in the first, non-literary half of his life, gave his writing a global reach and richness that none of his contemporaries could even begin to match. A young diplomat named John Buchan put it well in his insightful review of what was arguably Conrad’s greatest novel, Nostromo. The former sea captain, he wrote, simply “has a greater range of knowledge… of the strange ways of the world than any contemporary writer”.

For VS Naipaul, Conrad was the man who always preceded him in every place he visited. For Jasanoff, Conrad remains the man who, thanks to his prophetic sweep, in many ways precedes us all: his world is ours, she implies, and vice versa: Conrad, she writes, was the pioneer – the first “to grapple with the ramifications of living in a global world: the moral and material impact of dislocation, the tensions and opportunities of multi-ethnic societies, the disruption wrought by technological change… Conrad believed that people could never really escape the constraints of forces bigger than themselves.” Using, as she puts it, “the compass of the historian, the chart of the biographer and the navigational sextant of the fiction reader”, she redefines the role Conrad played in helping us to comprehend the unequal, violent globalised world we live in. In this she succeeds brilliantly, and the result is an extraordinary and profoundly ambitious book, little short of a masterpiece.

• The Dawn Watch: Joseph Conrad in a Global World by Maya Jasanoff is published by William Collins (£25). To order a copy for £21.25 go to guardianbookshop.com or call 0330 333 6846