The sentence was far in excess of what many in the financial world thought he might be given. He had cooperated fully with the Singapore authorities and pleaded guilty, thus avoiding a long and expensive trial.
But if Leeson felt double-crossed, he did not show it, merely sucking in his cheeks as the sentence was announced and going to jail stony-faced.
The sentence, just one-and-a- half years below the maximum, was pronounced by the senior district court judge Richard Magnus, who has a reputation for harsh sentencing.
It should herald the end of the Leeson family's nightmare, his father- in-law, Alec Sims, said yesterday. But a spokesman for Barings' bondholders said the group wanted new civil actions over the case, and dismissed the Singapore trial as "a sideshow".
"This is not a show that is going to close very quickly - I am afraid it may become the legal equivalent of The Mousetrap," said Jonathan Stone, chairman of the Perpetual Noteholders Action Group.
Mr Sims, father of Leeson's wife, Lisa, said that the family was very disappointed at the sentence, but added that the 28-year-old was strong enough to cope with his new life.
Leeson will serve his sentence in one of Singapore's four high-security jails, and is unlikely to serve more than three years and five months, after remission for good behaviour and the time spent on remand in Germany is taken into consideration.
In a sombre judgement delivered without any British-style flourishes or eccentricities, Mr Magnus, a Singaporean Indian, explained that "where very large sums of money are involved, a lengthy sentence of imprisonment is warranted".
He said that Leeson had "spun a web of deceit" around his unauthorised trades in Japanese stock market futures. Leeson was not on trial for gambling away billions of dollars but for hiding the extent of his losses from Barings' auditors and Simex, the Singapore International Monetary Exchange.
However, Leeson had caused Simex to return almost S$115m dollars (pounds 53m) which it was entitled to keep as security against bad debt, and he had pleaded guilty to a further nine charges involving the fraudulent exchange of some S$256 million.
The focus of attention will now switch to Leeson's superiors - the men named in the Singapore independent investigators' report into the collapse of Barings. They are Peter Norris, the former chief executive officer of the Baring Investment Bank Group, who is held most responsible for covering up Leeson's losses and may face extradition from London; and Leeson's two immediate superiors in Singapore, James Bax and Simon Jones. Both men have had their passports confiscated by the Singaporean authorities.
As he settles down to prison life, in a cell shared with two other men and practically no privacy, Leeson may be consoled by the thought of what his former bosses are facing.
Mr Norris, well known in investment circles as a man of extreme self- confidence, with a reputation for turning round difficult situations, was brought in to restore profitability to the division. The paper profits made by the rogue trader Leeson in Singapore were playing a major role in helping to meet this.
Leeson is uniquely placed to give testimony on his relationship with his superiors, which should go some way to explain how his losses were concealed for so long and why the parent company kept funnelling money into Singapore to cover the losses.