The bank will run applications from a remote server with thin clients, which use less power and space than PCs and offer flexible working through full desktop functionality over the internet. Barclays said thin clients use 73% less power overall than standard PCs.
The bank is using VMware's Virtual Desktop Infrastructure with Windows XP running on virtual machines.
The initial implementation of 4,240 thin clients at Barclays Capital is due to be completed early next year, and a further 6,000-desktop roll-out is being considered as the bank looks to extend the strategy to Barclays Wealth and Barclays Global Investors.
The PCs being replaced will be re-used in other parts of the business or recycled, said a Barclays spokesman.
As well as improving the bank's green credentials, the roll-out at Barclays Capital offers flexibility and quick execution in a period of rapid growth, said the bank. "Its success will be replicated across the other parts of the Barclays Group," it said.
Following a pilot involving 150 users, the implementation began in August with more than 1,000 thin clients placed in offices in London, the US and Singapore. Another 800 will be put into sites in London later this year, and the first phase of the roll-out will be completed early next year with 200 more units in London.
Explaining the business case for the implementation, the bank said, "Barclays is carbon neutral in the UK, and it is working towards becoming carbon neutral globally. Partly, that is about being a good corporate citizen, but a big part of our motivation is that it simply makes good economic sense.
"Reducing our costs is always good for business, and in IT in particular there are extremely attractive savings to be made."
Barclays said support costs would be reduced because thin clients are self-configuring, simple to move, and require a reduced skill set to deploy. As well as using less power than standard PCs, the bank said the thin clients would have a longer lifespan.