It was the early 1990s in an era of massive salaries, profits and bonuses and the boy from working class Watford in the UK, was the rising star of Barings bank - a 233-year-old instutitution which counted the Queen among its clients.
"It was all very exciting, it was always changing, no two days were the same," Mr Leeson said from his home in Ireland.
"It was a landscape of opportunity ... Banks were getting bigger, people needed to work in the city and I suppose in many ways it was a bit of a land grab going on. People were moving into new markets, new products. It was a wealth of opportunity."
His job was to trade on the future price of Japan's Nikkei 225 index, a complex feat that quickly earned him a stellar reputation - said to be responsible for up to 10 per cent of the bank's annual income.
But behind the scenes, Leeson was living a double life.
"I often liken it to a Jekyl and Hyde type of existence because nobody knew more clearly than me what was really happening but everybody was buying into the success story which was fabricated. So it was like leading two different lives and reacting two different ways depending on where I was and who I was with."
Financial markets were moving aggressively in a way that the Singapore exchange couldn't always keep pace with.
Leeson said while traders typically like to "match" their trades within 30 minutes, in some cases this wasn't being done until 12-14 hours after a trade was completed.
At one point, he realised a colleague had made a grave mistake.
But rather than report it to bosses in London, Leeson hid the losses in a separate account known as the 'five eights' account for their lucky reputation in Chinese culture.
"I believed the next day the market would get back to that sort of level and I would be able to close the trade off without anybody really knowing about what was going on," he said.
"That didn't happen, it got considerably worse during the day. Over a period it got worse and worse."