The 119-year-old lender has reported more than $3bn in mortgage writedowns and loan losses since the start of the credit crisis last summer following a misguided spree in the US sub-prime market.
Its share value has fallen by 74% since last year, falling to just $9 on Friday 4 April before recovering again to $13.26 on news of the rescue package.
Washington Mutual has already cut 3,000 jobs and raised $3.7bn via a rights issue.
Reports from the US suggests that the lender is set to withdraw from the wholesale lending business and close all its stand-alone home loan centres. As a result WaMu loans would no longer be available through intermediaries, though they would still be available through branches or on line.
News of the deal coincided with the announcement that the US Federal Reserve was offering $50bn in 28-day credit through its Term Auction Facility. The minimum possible bid is $5m and the maximum is $5bn with amounts being available at $100,000 tranches.
This auction is one of many that has been offered by the Fed since December in an effort to inject liquidity into the markets and stave off further turmoil. Similar actions have been taken by the Bank of England and the European Central Bank for the same reasons.