Peter Doyle said in a letter to the IMF executive board that he wanted to explain his resignation after 20 years.
He writes of “incompetence”, “failings” and “disastrous” appointments for the IMF’s managing director, stretching back 10 years.
No one from the Washington-based IMF was immediately available for comment.
Mr. Doyle, former adviser to the IMF’s European Department, which is running the bailout programs for Greece, Portugal and Ireland, said the Fund’s delay in warning about the urgency of the global financial crisis was a failure of the “first order”.
In the letter, dated 18 June and obtained by the US broadcaster CNN, Mr. Doyle said the failings of IMF surveillance of the financial crisis “are, if anything, becoming more deeply entrenched”.
He writes: “This fact is most clear in regard to appointments for managing director which, over the past decade, have all-too-evidently been disastrous.
“Even the current incumbent [Christine Lagarde] is tainted, as neither her gender, integrity, nor elan can make up for the fundamental illegitimacy of the selection process.”
Mr. Doyle is thought to be echoing here widespread criticism that the head of the IMF is always a European, while the World Bank chief is always a US appointee.
Mr. Doyle concludes his letter: “There are good salty people here. But this one is moving on. You might want to take care not to lose the others.”
The IMF could not be reached immediately by the BBC. However, CNN reported that a Fund spokesman told it that there was nothing to substantiate Mr. Doyle’s claims and that the IMF had held its own investigations into surveillance of the financial crisis.