ABC News

President Obama will name his current chief of staff Jack Lew for Treasury secretary, replacing Timothy Geithner, according to knowledgeable sources.

An announcement is expected as early as tomorrow.

As chief of staff for the past year and budget director before that, Lew has been intimately involved in the negotiations with Congress on the debt ceiling, averting a government shutdown and the fiscal cliff - experience that will come in handy the from the moment he is confirmed.

Officials familiar with the selection process say Lew was the only person under serious consideration to replace Timothy Geithner as Treasury secretary. The primary factor: His ability to get right to work on the first crises likely to face the next Treasury secretary: the upcoming showdown with Congress over the debt ceiling (which will need to be raised in a matter of weeks) and automatic spending cuts set to take effect March 2. Another factor was Lew's experience as Bill Clinton's budget director, when he helped craft a bipartisan budget agreement that led to three years of budget surpluses.

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Lew also has private sector experience. Before joining the Obama Administration in 2009 as deputy secretary of state, he served as the chief operating officer of Citigroup's Global Wealth Management and Alternative Investments divisions.

Lew is an orthodox Jew who strictly observes the Sabbath: he leaves work at sundown every Friday and does not work on Saturday.