Standard Life Bank, which opened 11 years ago as an offshoot of Standard Life, a Scottish life insurance company, will be swallowed up by the larger UK bank, with its name being dropped and its employees transferring to Barclays.
Barclays will acquire a savings book worth around $9 billion and a mortgage book worth more than $14 billion as part of the deal.
The two companies have also agreed to enter a strategic initiative to explore joint opportunities in the UK financial sector.
Frits Seegers, chief executive of Barclays Global Retail and Commercial Banking, said: "We believe that we will be able to drive significant value for customers and shareholders - both through this acquisition and through the strategic initiative."
Standard Life Bank reported pre-tax profits of $24.5 million for the first six months of 2009, following a profit of $42.5 million for the bank in 2008.
Sir Sandy Crombie, group chief executive of Standard Life, said the sale was agreed after his company decided the activities of its banking arm were no longer consistent with its long-term financial objectives.
The deal, which is subject to regulatory approval, is set to go through in early 2010.
By Asim Shah