The man named in media reports as Kweku Adoboli, 31, was arrested at his desk at UBS's offices in central London at 3.30am.
Adoboli, of Ghanaian descent, is being blamed for losing the bank $2.0 billion (€1.46 billion) through unauthorised trading.
He is listed as director of Exchange Traded Funds (ETF) and Delta-1 Trading at UBS Investment Bank in his profile on LinkedIn, the social networking site for professionals.
ETFs are shares that can be traded and that track movements in other indexes, meaning they are susceptible to short-term volatility in prices.
Adoboli graduated from the University of Nottingham in central England with a degree in computer science in 2003 and, according to the Financial Services Authority (FSA) watchdog, joined UBS in 2006 as a trainee investment adviser.
Many accounts described a confident man who enjoyed flaunting his wealth with lavish parties at his former flat in the trendy Shoreditch area of east London.
"He came across as someone who worked quite hard to get where he was and played quite hard too," one former colleague told the Financial Times.
Philip Octave, Adoboli's former landlord, said the trader paid £1,000 ($1,580) a week in rent for the flat and was "well spoken and dressed very smartly".
City of London Police commander Ian Dyson said officers had made the arrest after being tipped off by UBS at 1.00am when the alleged rogue trade surfaced.
Police refused to confirm the suspect's identity, in keeping with standard British practice.
An FSA spokesman said: "At this stage it's a police investigation only, which is at a very early stage... We are not commenting at all on what our next steps could be."