The proposals, originally announced by Treasury secretary Henry Paulson following a loss of market confidence in the lenders two weeks ago, should now safeguard the future of the organisations.
Around $300 billion in loans will now be guaranteed - helping to alleviate the pressure on the US housing market.
Connecticut Democrat Christopher Dodd, principle author of the housing bill, commented: "This legislation won't perform miracles. But as others have said, it's a step - and I hope an important step - to putting our nation on the road to economic recovery."
However, Iowa Republican Charles Grassley, R-Iowa sounded a note of caution - pointing out that the rescue plan might not represent good value for money.
"This bill has fallen prey to the special interests on Wall Street and K Street at an unjustifiable expense to taxpayers and homeowners on Main Street," he said.
Collectively, Fannie and Freddie hold over 50 per cent of total US mortgage debt - guaranteeing between them around $2.5 trillion.