On Tuesday Barclays shocked the City when it announced it had taken a pounds 250m hit this year because of losses on investments in the Russian Treasury Bill market.
The loss was by far the biggest disclosed by a British bank as a result of the Russian financial crisis, and on a par with some of the big US investment banks who between them have lost billions of dollars over the past few weeks.
Ms Harrington, an American who joined the firm from Goldman Sachs last February, said last night: "I have accepted another position and I plan on taking a month or more of leave before I take it up." She refused to say where she was going or what the new job entailed. A spokesman for Barclays Capital said last night: "We are making no comment on that story."
However, the decision is believed to have come as a complete surprise to colleagues.
Since Tuesday's announcement there has been speculation that Barclays may now decide to cut back on its bond trading business because of the setback. Barclays has already pulled out of equity and corporate advisory business, the former BZW, which it sold to Credit Suisse First Boston.
Barclays' chief executive, Martin Taylor, said earlier this week that he saw no reason to reverse the bank's commitment to develop Barclays Capital, despite the widespread criticism over these losses.
However, analysts said they thought it was inevitable that after the pounds 250m hit it had taken, Barclays' board would think twice about committing more capital to the business.