Semi-invisible Man, by Julian Evans

Graham Greene, in a quote used on later editions of Norman Lewis's work, described his younger contemporary as "one of the best writers not just of any particular decade, but of our century". Sadly, the response of most British readers on hearing his name is likely to be that of the woman who worked in the publicity department of his one-time publisher, Collins: "Norman who?" In the words of the critic JW Lambert, Lewis was a writer who failed to break through "the mysterious barrier separating the admired from the famous".

Now, in the centenary of his birth, Julian Evans has brought out a massive biography that allows for the first time a proper assessment of Lewis's remarkable career. Evans, who edited Lewis's work and was a friend for over 16 years, would seem the ideal person to write such a book. But, as he confesses, he initially did not want to, and explains why in an introduction whose references range from Machiavelli and Kundera to the "Calvinist doctrine of the human being's 'inner space'". His prose at first is so dense and intellectual that you might question his suitability as the biographer of a writer whose hallmarks were lucidity, modesty, understatement, lack of pretension, and a preference for life lived beyond the precious confines of the literary world.

Yet, as Evans gets into his stride, any doubts about him and his undertaking soon vanish. The quietly compelling personality of Lewis takes over, as does Evans's unfailingly sympathetic and perceptive view of the man and his work. Lewis, notoriously, was not given to personal revelations; and you might wonder how much more can be said about his life other than what he chose to reveal in his memoirs and travel books. However, through a mixture of empathy and thorough research, Evans fills in many gaps. Thus while Lewis's hugely enjoyable autobiography Jackdaw Cake tells us about his eccentric family in Enfield and Wales, Evans uncovers "bullying" and other unspoken aspects of a suburban childhood destined to inspire a wish to escape.

The "semi-invisible man", we also find, had a youth in many ways as showy as his first attempts at prose. He loved guns, Bugattis and Porsches, went motor racing, and treated guests to displays of shooting practice in his London sitting-room. Perhaps the most surprising discovery is of Lewis's complex, overlapping relationships, which might partly account for the secretiveness of his nature.

Admirably, Evans is interested in the personal details only insofar as they reflect on what he rightly considers the most important part of a literary biography – the subject's writings. The factors that make Lewis one of the finest British travel writers of the 20th century are all here, beginning with his fluency in several languages, the breadth of his knowledge, and the powers of observation resulting from his training as a photographer. As with other great writers about place, he eschewed the obvious, allowed himself to be governed by instinct, and had a tendency to attract what Evans calls "baroque accidents of chance". Above all, Lewis had an extraordinary gift of getting on with all kinds of people. Classless, lacking in snobbery, and with an "intense and very un-British enthusiasm", he differed from so many other British travellers by adapting discreetly to any situation, never assuming a stance of scornful superiority, and by freeing himself as much as possible from the attitudes and prejudices of a British middle-class education.

A first marriage to a passionate woman from a Sicilian-Spanish family with Mafia connections brought out some of the more salient aspects of his personality. But it was his "raw experiences" as an intelligence officer during the Second World War that did more than anything else to encourage his aspirations to be a writer. In the anti-climactic aftermath, he assuaged his growing restlessness by embarking on a long line of adventure-filled novels with exotic settings. At the same time he started staying in Spain (which allowed him, he said, "to get away from the insipidity of modern times"), and had a first and almost last taste of instant success with two politically incisive books about Asia, A Dragon Apparent and Golden Earth.

It says much of Lewis's idiosyncratic position as a writer that the next major phase of his career should begin with his protracted old age. As he advanced into his sixties, he could easily have ended up a forgotten figure. However, he was kept going by a small group of devotees, among whom was Peter Crookston, an editor at the Sunday Times and later the Observer, who sent Lewis on assignments to some of the remotest parts of the world. A daring traveller almost until his nineties, Lewis developed an obsession with the survival of primitive tribes, whom he wrote about with characteristically restrained passion, and increasing romantic self-identification.

Fame seemed at last to await Lewis in his seventies, when he wrote some of his best books, and had some earlier ones reissued to great acclaim by the visionary founder of Eland Books, John Hatt. He gave his first interview, aged 76, and was awarded his first prize. Nonetheless he was not good at promoting himself, being too reticent and self-effacing, and having a voice which a producer once told me was not "suitable for radio". And, for all the publicity, his masterly wartime memoir Naples 44 did only moderately well to begin with, as did his nostalgic account of Spanish village life, Voices from the Old Sea. The latter got far less attention in Britain's literary pages than Eric Newby's bland On the Shores of the Mediterranean.

Perhaps the true measure of Lewis's greatness was that he did not allow himself to be embittered. A depressing encounter with Hemingway in Cuba had taught him the dangers of literary celebrity, and made him perhaps aware of the advantages of his own position. He had the freedom to do whatever he wanted, and a perpetual sense of wonder. And he has now been rewarded with a profound and stimulating biography which will probably ensure the continuing appreciation of his works long after some of the unjustly famous writers of today have been forgotten.

Michael Jacobs's latest book is 'Ghost Train through the Andes' (Murray)