At the signing ceremony in the Oval Office, Trump called it "a bill for the middle class and a bill for jobs," adding "corporations are literally going wild", reported Xinhua.
Hailing the size of the tax cut, Trump said he was going to wait to sign it until after January 1, but changed his mind. The Independent reported that before he signed, Trump told reporters that "the numbers will speak".
The legislation provides generous cuts for corporations and the wealthiest Americans and smaller ones for the middle class and low-income families.
On Wednesday, the US Congress passed the Republican bill on expected lines, with no Democrat voting for it. "By cutting taxes and reforming the broken system, we are now pouring rocket fuel into the engine of our economy," Xinhua quoted Trump as saying on Wednesday.
Some companies said they would spend the savings from lower corporate taxes on higher wages and new construction.
Cutting corporate income tax rates to 21 per cent from the current 35 per cent and lowering individual income rates, it is the first major overhaul of the US' tax laws since 1986, but far from the largest tax cut in its history, as Trump claims, said the Independent.
Politically, it marks the Republicans' first major legislative accomplishment of the Trump presidency.