UBS trader Kweku Adoboli, who gambled away $2.3 billion of the Swiss bank's money, was found guilty of one count of fraud in London on Tuesday.
The jury at Southwark Crown Court was still deliberating on one other charge of fraud and four counts of false accounting between October 2008 and September 2011.
The Ghanaian-born trader, 32, who stands accused of Britain's biggest ever fraud, admitted the losses but denied any wrongdoing.
During the two-month trial he claimed senior managers were fully aware of his activities and encouraged him to take risks to make profits for UBS.
But prosecutors claim that in a bid to boost his status and bonuses Adoboli exceeded his trading limits, failed to hedge trades and faked records to cover his tracks.
The court heard had that at one point he was at risk of causing the bank losses of $12 billion.
Prosecution lawyer Sasha Wass told jurors during the trial that he was "a gamble or two away from destroying Switzerland's largest bank for his own gain".
"Mr Adoboli's motive for this behaviour was to increase his bonus, his status within the bank, his job prospects and of course his ego," she said.
Adoboli, the privately-educated son of a former UN official, told jurors that he had dedicated his life to benefiting the bank and viewed his colleagues at UBS's London offices as "family".