Michael Ridpath, 32, has already signed deals worth pounds 750,000 - thought to be a record for a British first novel - and interest in the film rights has come from Hollywood.
Free to Trade, a story of dishonesty and financial crime in the world of City traders, has aroused worldwide interest and Mr Ridpath has already contracted to write a second novel.
The former trader, who now works for the venture capital company Apax Partners, began the novel in the summer of 1990. 'I wrote the first chapter of a book as a sort of exercise and really enjoyed it, and I kept going as a relaxation really,' he said.
His only previous experience was writing history essays at university in Oxford and company reports - 'that taught me to write clearly' - but he read teach-yourself books on novel writing, studied Dick Francis and other thriller writers and asked his wife and friends for comments on his first draft.
Mr Ridpath, who lives in Finchley, north London, said he thought he had stumbled on a gap in the market for 'white-collar thrillers'.
'I think finance is exciting, and I've tried to make it as exciting as possible without too much greed, glamour and conspicuous consumption. A lot of people in the City are not greedy, they're very competitive. It's that which causes them to be dishonest,' he said.
Carole Blake, of his agents Blake Friedmann, said the novel was a one-in-a-million find among the 30 or so unsolicited manuscripts she receives daily.
'It's a combination of very, very, good writing which reads effortlessly, a damn good story and very good characters that you're interested in - page-turning qualities,' she said.
Within a week of meeting Mr Ridpath she had sent the manuscript to publishers, and received the first offer.
Heinemann beat four other British publishers to secure the book for pounds 250,000. Foreign deals are worth another pounds 500,000 and Ms Blake said others were likely to take the total to pounds 1m.
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