"Mistakes were made at AIG on a scale that few could have imagined possible," Edward Liddy will tell a Congressional hearing later on Wednesday.
He will also admit that AIG is "too complex, too unwieldy and too opaque".
Mr Liddy also calls the $165m (£119m) bonuses paid by AIG "distasteful" after the insurer took about $170bn of aid from the US government.
Mr Liddy is to appear in front of Congressional committee to answer questions about the bonuses and the plight of AIG.
Before Mr Liddy appeared before the committee, members of the committee expressed their anger, not just at the bonuses paid to AIG executives, but also at the $170bn bail-out by the US government.
One referred to a "tidal wave of rage" throughout the US, while another called the US taxpayer "the ultimate sucker" in the whole AIG saga.