Christine Lagarde, the French finance minister, was late on Tuesday elected as the first woman to head the IMF. Her victory was sealed after a late endorsement from the US which saw her beat Mexican central bank governor Agustin Carstens to the post.

Lagarde, who succeeds Dominique Strauss Kahn following his resignation in May to deal with sexual assault allegations, is said to be facing tough challenges in the wake of the debt crisis surrounding several European nations.

Immediately after her appointment Lagarde urged Greek ministers, who are due to vote on austerity measures worth €28.4bn on Wednesday, to unite so as to avoid default. The austerity package of taxes, spending cuts and sell-offs is critical for Greece to secure international aid from the ECB and IMF.

“If I have one message tonight for Greece, it is to call on the Greek political opposition to support the party in power in a spirit of national unity,” she said.