Lagarde's selection became all but assured when the Obama administration endorsed her earlier Tuesday. Hours later, the IMF's 24-member board voted to appoint her to the position. She had also won support from Europe, China and Russia.
Lagarde takes over at a tumultuous time. Europe's debt crisis is intensifying. Emerging nations want a greater voice at the IMF. And the organization's reputation has been tarred by a scandal involving Dominique Strauss-Kahn, whom she replaces as leader.
Strauss-Kahn resigned last month after being charged with sexually assaulting a New York City hotel housekeeper.