Barclays chief executive Bob Diamond quit with immediate effect on Tuesday over an interest rate-rigging scandal, becoming the highest-profile victim so far in a probe that spans a dozen major banks across the world.
Britain's third-largest bank said that outgoing chairman Marcus Agius - who himself announced his departure a day earlier - would lead the search for a new executive.
"The external pressure placed on Barclays has reached a level that risks damaging the franchise - I cannot let that happen," Diamond said in a statement.
Agius announced his resignation on Monday in the scandal over traders manipulating the London Interbank Offered Rate (Libor), which is used worldwide as a benchmark for prices on about $350 trillion of financial products.
But Agius said he would stay in office as long as the search for a new chairman continued.
Barclays was fined $453 million by U.S. and British authorities, becoming the first bank to settle in an investigation that is looking at more than a dozen others, including Citigroup, UBS and RBS.