After university, Keay went into advertising at the birth of swinging 60s London, which he did for four years.
"I was never at the cutting edge but the money was good. I knew I was filling in time and eventually I got fed up," he says.
He quit and went on holiday in Kashmir, which began his long and passionate interest in Asia.
He eventually based himself there, and began writing to "pay the rent". This led to him being a freelance writer for The Economist, for whom he covered Indira Gandhi's victory in the 1971 General Election.
Keay was then recruited by the BBC to present a series of radio documentaries looking at cultural aspects of many areas of the world, many of which were in Southeast Asia. He says it didn't always feel appropriate to focus just on the arts.
"I remember Burma being quite harrowing and having to be quite clandestine. Having asked someone to risk their life to be interviewed it wasn't really appropriate to ask them about Burmese theater puppets," he says.
It was in the late-1970s that he began to establish himself as a writer. Not attached to any university he sees himself as a "history writer" rather than an academic historian.
He is therefore in good company, since Edward Gibbon (The Decline and Fall of the Roman Empire) and Thomas Carlyle (The French Revolution) would be categorized similarly.
"They were writers who wrote about history. I have difficulty with this term 'historian'. It always seems to me the best history is written by people who aren't historians. Neither Gibbon or Carlyle would be qualified historians in today's terms," he says.
He says researching China's history was different from that of India, the subject of his previous book.
"They are complete opposites in a way. China is a country that has had a sense of identity and being united since the year dot. India, by contrast has consisted of dozens of separate kingdoms. Geographically, it is still divided between three or four nation states and still is obsessed with unity and diversity."
He says one of the advantages of researching China history is that everything is written down over a period that spans a large part of human civilization.
"Dates are verifiable in China back to the 8th century BC, whereas the first recorded date in Indian history of which we are reasonably confident is in the 9th century AD," he says.
Keay says one of the golden eras of Chinese history is widely acknowledged to be the Tang period from AD 618 to 907, which saw the emergence of the Silk Route and caravan trains bringing goods like dates, saffron and glass bottles to China. But he argues there is a certain mythology surrounding this period too.
"The successful bit of the Tang period with all the exotic goods arriving was 50 to 100 years. The rest of the period was total chaos," he says.
Keay says the common notion that the first emperor in any dynastic period is the key figures is not really true either.
"The founding emperor is often a kind of ambiguous character. It is usually the second, third or fourth emperor who extends the power of the dynasty before a long period of decline sets in," he says.
Keay says there is a danger for anyone taking on the full sweep of China history in giving too much prominence to the teachings of Confucius.
"There is a quote in the first Analects: 'Is it not a pleasure, having learned something, to try it out at due intervals? Is it not a joy to have like-minded friends come from afar?' Well, wonderful!" he laughs.
"He slightly reminds me of Dr (Samuel) Johnson throwing out all these quotes all the time with all these Boswells around him writing them down. Every now and again he says something prosaic as we all do.
"It is written down as though it is full of mysterious meaning and all the chap was saying was that he needed a drink or something."
Keay argues in the book that the commonly held view that China got left behind in the 19th century after Western societies industrialized is misleading.
"The 1870s were actually a period of regeneration for China as various Chinese people go to America and learn about new manufacturing techniques and then start producing the stuff themselves," he says.
Keay says researching the history of China has given him a certain confidence about the future.
He says that if China does emerge as a superpower in the 21st century it will not want to disrupt the global order.
"I think history teaches us that a world in which China is a superpower might not be as uncomfortable as many people think. I don't think China feels the need to assert itself militarily and physically as many countries in the West have," he says.
China, A History by John Keay (Harper Collins)