Robert Byron is the travel writer's travel writer. Between the wars, he motored across the Balkans in an open-topped Sunbeam and galloped over the central Asian steppe on a wooden saddle, a notebook in one pocket and a glass jar of Fortnum's chicken in aspic in the other. His books still dazzle. Like Kinglake, Curzon and Norman Douglas, he was an exponent of the fine English tradition that upheld travel as a learned pursuit.

He was born in 1905 in Wembley, hardly a cradle of the fine architecture that he came to worship. His father, a civil engineer, was perennially short of cash, but still, he managed to despatch the boy to Eton. After Oxford (he was booted out, but right at the end of his studies) the young Byron moved to London and began a career in journalism, making a strong start by getting sacked from the Daily Mail. From then on, he travelled and wrote continually, producing a robust body of articles (many for this magazine), travel books, works on art and even a jointly authored comic novel. He was also a stylish draughtsman and a talented photographer, loitering among the ruins with a sketchbook and cumbersome camera in a tin box, like a true Victorian.

The early journeys were unpromising. "How horrible most of Europe is," he complained to Henry Yorke (aka Henry Green), the only friend who was a better writer than he. But things looked up. He loved Mount Athos, where the Byzantine frescoes in the tiny barrel-vaulted chapels fuelled his gathering prejudice against classical art. The following year he motored around Spain in a green Bentley to study El Greco, Gavin Henderson at the wheel, slowing down from 70 to 50 only to swig from a bottle of Vouvray.

He looked like Queen Victoria - short, with a yellowish complexion, a pudgy face and slightly popping eyes. Highly strung by nature, Byron was easily bored, often bad-tempered and regularly rude. He loved collecting beautiful things, had immaculate taste and was fascinated by clothes and fabrics. Above all, he had a passion for architecture that remained constant throughout his life. Knox has a keen appreciation of the architectural zeitgeist, as any writer on Byron must.

In his travel books, as Knox shows, Byron early on established the method of suggesting the spontaneity of speech through quick-fire and often unattributed dialogue. This was developed to great effect in the later works, notably in his masterpiece, The Road to Oxiana. Of his day, he was a heartbreaking writer, and one who treated ancient buildings and modern people as two facets of a continuing story. Of The Station Knox comments perceptively, "He made Athos his own", which is what all the best travel writers do with the landscapes they love.

The story benefits from a lively cast including Nancy Mitford, James Lees-Milne and Evelyn Waugh, who named Byron as one of five young writers to embody the spirit of their generation. Byron consistently and unsuccessfully tried to seduce Waugh, until they finally had a punch-up in a lift. There is not much on the affairs that did come off (in parti-cular one longs to know more about the "Japanese train attendant"), though Knox is good on Byron's greatest love, Desmond Parsons, brother of the sixth Earl of Rosse ("You remain the pattern, the zenith of all the world can give me," Byron wrote to him longingly before Parsons died of Hodgkin's disease at the age of 26). In the end one has no real sense of the interior life; but perhaps this is a lot to ask.

This is a thoroughly researched book, solid in content. Knox is reluctant to form judgements and allows the facts to speak for themselves instead. In the matter of style, he is less sure of himself. Much of the narrative is wooden ("And so his days at Eton drew to a close") and he has a fondness for cliche (several characters are "bowled over", tempers "begin to fray" and friends appear "in hot pursuit"), which is ironic in the light of what Anthony Powell called Byron's "obsessive repugnance for cliche". And I wish biographers wouldn't refer to their subjects by their Christian name: the faux intimacy never works.

None the less, the prose warms up in the second half and there are beguiling touches - we glimpse our man in Venice, "growling at waiters and German holidaymakers", and after Lord Jersey's dazzling fete champetre in 1939, writes Knox, "Illumined, thus, in the flashlight of notoriety, the Georgian Group took a final swaggering bow before the curtain came crashing down upon its world." (Byron was active in the founding of the group, "a crusader in the battle to save Georgian London".)

As the horror of the late 1930s unfolded in Germany, Byron became an obsessive, almost hysterical opponent of fascism, appeasement and anyone who supported either. When war finally came, he hurled himself with customary vigour into politics and in particular propaganda, arguing for the creation of a union of states to preserve world peace after the defeat of Germany. In the guise of a Sunday Times war correspondent he was commissioned to travel to Meshed, in Iran, as an observer and sailed out of Liverpool in February 1941. A U-boat torpedoed his ship and he was drowned two days before his 36th birthday. The last pages of this engrossing book are beautifully done, a threnody for the talent extinguished by war.

Sara Wheeler's most recent book is Cherry: a life of Apsley Cherry-Garrard (Vintage)