Social crusader, scandal-monger, hater of the bourgeoisie and champion of the oppressed, Zola casts a long shadow down the century. Jonathan Keates reads an epic biography
When Zola visited London in 1893 as guest of honour at the annual congress of the Institute of Journalists, he was met at Victoria Station by the proprietor of the Daily Telegraph who, shaking the novelist warmly by the hand in the presence of numerous onlookers, spoke of ''the feelings of respect and admiration which your marvellous fecundity inspires''.

Oscar Wilde sent him flowers and there was a ball at the Guildhall with the Lord Mayor in full fig, where a French correspondent described the author of Le Debacle passing bemused amid a crowd shouting ''Zola! Zola! Hurrah!'', its foremost ranks composed of young ladies dressed in white, whose ''large, naive, pure eyes, that had never read the things written by the honoured gentleman, intently devoured him''. Even if something which called itself the National Vigilance Association had earlier successfully doomed the English publisher of his novel La Terre to bankruptcy and imprisonment, Zola was now in forgiving mood and concluded a stirring speech at an official banquet with a toast to ''the universal fellowship of authors in the republic of letters''.

It is hard to imagine a modern British newspaper proprietor taking the trouble in person to meet a foreign novelist off the train, let alone a crowd gathering to applaud. What had Zola done to achieve such acclaim, and why, in his own age, did his resounding success dwarf those of Balzac and Flaubert, his fellow gods in the French fictional pantheon?

His beginnings were hardly promising. Zola pere, visionary and spendthrift, described in one official document as ''engineer-architect-topographer'', died when Emile was two, leaving the boy's mother with a mountain of debts and lawsuits. The greatest blessing of his undistinguished schooldays in the stuffy timewarp of Aix-en-Provence was a friendship with a large, ungainly youth, son of a wealthy hatter turned banker, named Paul Cezanne. It was to last more or less unbroken for forty years until Zola published his novel L'Oeuvre, the story of a provincial artist confronting ''the frightful phenomenon of artistic impotence'' by hanging himself in front of the massive unfinished painting of the Ile de la Cite on which he had been toiling in the midst of increasing domestic agonies. Monet, who read the novel as soon as it came out, told his friend Pissarro, ''I don't believe it will do us any harm; it's just a novel in which the author of Germinal came up short, that's all'', while Renoir regretted that Zola had been still more realistic in his portrayal of studio life. Cezanne, on the other hand, never spoke to Zola again. Even after the novelist's death, the dealer Ambroise Vollard reported, L'Oeuvre's criticism continued to bite. Angrily destroying a newly completed self-portrait, Cezanne snarled ''How could he dare say that a painter is done for because he has painted one bad picture?''

L'Oeuvre is itself an indifferent fictional canvas, but by the time it appeared in 1886, anything by Zola was an event. The crucial moment in his earlier career, after moving to Paris and becoming an advertising manager for Hachette, was the composition of Therese Raquin in 1867. This was indeed the succes d'horreur he foretold, a chronicle of murder and adultery in a petit-bourgeois family living inside a glass-roofed arcade whose grimy resistance to the daylight becomes the perfect symbol of lies and suppressions. Several of the book's features - its half-gloating, half-appalled treatment of sexual appetite and its embrace of theoretical ideas as to human behaviour - became trademarks of the mature Zola in the 20-book Rougon-Macquart cycle, a systematic study of a family's degeneration into "moral monsters'', on which he embarked a year after Therese Raquin.

By then he had taken his place alongside Flaubert and the Goncourts as a pernicious peddler of what Le Figaro's reviewer called ''la litterature putride''. Even if the novel was hardly a bestseller (government interference forbade its sale by travelling vendors) Zola had arrived, and Therese acts as an effective signpost towards a creative maturity dedicated to interpreting the strange new discourse of nightmare and neuroses which galloping urbanisation forced on the 19th century.

At the other extreme of Zola's life - a significant bookend, as it were, to Germinal and L'Assommoir - stands his involvement in the Dreyfus affair which convulsed France during the late 1890s. Frederick Brown sensibly underlines the multifaceted nature of the novelist's commitment to the cause of tolerance and rational good sense against the bien-pensant baying for blood which had sent the hapless Jewish captain to Devil's Island. The salvo of denunciations in the famous L'Aurore article of 13 January 1898, each beginning with the words ''J'accuse'', was not simply an enlightened appeal to ''the knowledge that will alleviate human woe and bring mankind the happiness to which it is entitled,'' but a mark of Zola's continuing obsession with victims and outcasts doomed by bourgeois exclusivism and hypocrisy. We can hardly blame him for seeking refuge in Walton-on-Thames while the anti-Semites volleyed their hate-mail and cries of ''Go back to Venice!'' (alluding to his family origins) echoed down the boulevards.

The whole episode, culminating in some shameful fudges and whitewashing from the French government, is handled with tremendous exuberance in Frederick Brown's epic biography, Zola: A Life (Macmillan, pounds 25). Its immensity, the amplitude of reference and perspective and the sense of the biographer enjoying the challenge of marshalling his resources, are - well, there's no other word for it, Zolaesque. Everything, from Zola's short-sighted attacks on Manet for being technically incompetent, to the writer's menage a trois with the chambermaid Jeanne Rozerot and her employer, his wife Alexandrine, whom Edmond de Goncourt described as ''looking like a faded doll from a nearly bankrupt department store'', is investigated with what some may feel is excessive enthusiasm.

Though every 20th-century novelist, from Jean-Paul Sartre to Martin Amis, stands indebted to him, he is not quite the figure he was for our great- grandparents, and his style looks overloaded and galumphing beside many of his contemporaries. As a tribute to the visions he liberated and the moral integrity he asserted, however, Brown's monument to Zola is as handsome as he deserves.