The world lending body announced that the French finance minister would take over as managing director after a meeting of its 24-strong board in Washington.
The decisive factor in favour of Lagarde was the late formal backing of the United States. Brazil, China and Russia also said they would support her.
Traditionally Europe has always held the top IMF job, but developing countries had warned against a joint US-European deal.
In the end though several threw their weight behind Lagarde.
Her main rival, the Mexican Central Bank Governor Agustin Carstens, gained backing from some Latin American countries, Canada and Australia - but it was not enough.
Christine Lagarde takes over from fellow French national Dominique Strauss-Kahn who resigned.
While he concentrates on defending himself against sexual assault charges, she is likely to need all of her widely praised experience in handling the European debt crisis.
SOURCE: Euronews
