As a result, one client was charged an extra $8 million on $3.5 billion in currency trades, according to court documents.
In addition, the bank's head of currency trading in London is facing extradition in connection with the case, which is expected to shake-up the $5.3trn market, the Financial Times reports.
"This verdict makes clear that the defendant corruptly manipulated the foreign exchange market for the benefit of his bank and his bonus pool, to the detriment of the bank's client", said Acting Assistant Attorney General Blanco.
However, the suit was first brought to the U.S.to target individuals.
USA prosecutors have said that Mark Johnson, formerly head of HSBC's global foreign exchange cash trading desk, schemed to ramp up the price of British pounds before executing a trade for Cairn, making millions for HSBC at Cairn's expense.
He was arrested in July 2016 and indicted a month later in August.
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Prosecutors said that Cairn, which is an Edinburgh- based company began its relationship with HSBC in 2011. The oil and gas company had hired HSBC to convert the proceeds of an asset sale from dollars to pounds.
The prosecution built its case on certain telephone recordings between the parties.
They alleged that Johnson and Scott, on behalf of HSBC, bought sterling ahead of the deal, inflating the currency's value and ultimately netting a profit.
Shortly before the trade, Johnson and his co-conspirators took out proprietary positions on pound sterling, using the knowledge of the deal from the confidential information obtained from the client. He said that Johnson and his colleagues had tried to get a fair price for Cairn and even given Cairn a rebate. The court papers show that Johnson and Scott had discussed how far they could "ramp" the price of sterling against the dollar before their client would "squeal".
A former HSBC banker facing charges of fraudulently rigging a multi-billion dollar currency exchange deal was today convicted of fraud in a NY court.