JPMorgan has agreed to buy up most of the assets of the Seattle-based lender, which has been suffering from the deteriorating markets and concerns over its financial stability over recent weeks.
The deal comes to around $1.9 billion - and came about after WaMu was taken into the control of regulators.
WaMu encompasses around $307 billion in assets, making it the largest ever failed bank in the US.
The bank's depositors, who have withdrawn over $16 billion from it over the past week and a half due to the stability concerns, were assured that the business will not be affected.
"For bank customers, it will be a seamless transition," said Stella Blair, chairman of the Federal Deposit Insurance Agency.
She added: "Bank customers should expect business as usual come Friday morning."
The previous largest-ever bank failure was Continental Illinois, which required a government bailout in 1984.