President George W Bush's $350bn (£214bn) tax cutting package has become law after he signed the bill at a ceremony in the White House.
The figure is less than half the size the president originally proposed.
But he said it would help to boost the economy and create jobs.
The plan has been controversial because critics have argued that it will push the US further into the red, undermine the dollar and be of little help to many Americans.
Both houses of the US Congress approved the 10 year plan earlier this month.
But in the Senate, Vice-President Dick Cheney had to use his casting vote to get the scheme passed.
Jobs for all
At the signing ceremony, President Bush said he particularly wanted to thank members of the US Congress who had worked closely with the administration "to do what is right for the American people".
He said the plan had been supported by people who understood that tax cuts would help to create more jobs.
"We know that tax relief is going to help this economy because it's done so in the past.
"We're building on the strength of our economy so that everyone who wants to work can find a job."
The main plank of the bill is a staged cut in dividend and capital gains taxes.