Democrats have signaled they won't support the deal without additional protections for workers, though it calls for some more safeguards than the agreement it would replace. Each country's legislature must also approve the agreement.
The signing ceremony in and of itself represented a political victory for Trump, who has been eager to mark the deal with a formal photo opportunity alongside Canadian Prime Minister Justin Trudeau and outgoing Mexican President Enrique Peña Nieto.
But Trudeau, who considered not attending the ceremony that Trump was so eager for, refused to play along. He opted not to hold up the agreement to showcase the leaders' signatures.
The accord - called the United States-Mexico-Canada Agreement (USMCA) - requires 75 percent of auto content to be made in the NAFTA region, up from the current level of 62.5 percent, a move that would make it hard for automakers to use parts produced outside the three countries.
The pact overhauls the former North American Free Trade Agreement, which has for the last 25 years ensured the free movement of capital and goods across North American borders.
The president canceled on Putin not long after his former lawyer, Michael Cohen, revealed he had lied to Congress to cover up that he was negotiating a real estate deal in Moscow on Trump's behalf during the Republican presidential primary in 2016.
During a speech Friday, the president called the new agreement one of the largest deals to re-balance trade in recent history.
While Trump hailed the revised trade pact, Trudeau was more measured and used the event to call on Trump to remove the steel and aluminium tariffs the US slapped on Canada and Mexico. We've taken a lot of barbs and a little abuse, and we got there.
"Donald ... we need to keep working to remove the tariffs on steel and aluminum between our countries", Trudeau said.
While the leaders presented a united front, Trump's tearing up of the old NAFTA, which he has repeatedly ridiculed, was a shock to the system that prompted months of severe tensions between the long-peaceful neighbours. "You don't see that happen very often", he said. The agreement includes a new rule, for example, that a auto will only be freed from tariffs if 40 per cent or more of its contents are produced by workers earning $16 (U.S.) per hour or more.
The White House released remarks by the three leaders at the signing ceremony on its website.
With his "America First" approach, general distaste for multinational deals and habit of insulting allies, Trump typically gets a mixed reception at global gatherings. Renegotiating and reorganizing NAFTA into the USMCA is a positive development for our state, given the economic relationship and mutual reliance North Dakota and Canada share as neighbors.
Since then, the three sides have bickered over the wording and the finer points of the deal and still had not agreed just hours before officials were due to sit down and sign it as the G20 summit kicks off in Buenos Aires.
Senior Canadian officials said privately that in the negotiations, Trudeau had not been swayed by Trump's insults, feeling confident that Canada's view of an open, multilateral world order was the right path forward. And while we don't know the final details of the USMCA, we do know that it largely resembles, in many ways, what was there before.
Trump's Friday schedule also includes an informal meeting with Australia's new prime minister.