However, he lamented the deal doesn't remove tariffs on Canadian steel and aluminum, urging for more work to be done on this issue.
"In the U.S., the new trade pact will support high-paying manufacturing jobs and promote greater access for American exports across the range of sectors including our farming, manufacturing and service industries", Trump said.
Trump, who repeatedly branded NAFTA as the "worst trade deal ever made", said earlier he will not back down from his pledge for the USA to quit the agreement, if his concerns were not met. "We make new deal or go back to pre-NAFTA!" he said. And Trump is facing a House of Representatives controlled by the Democrats.
The Council of Canadians' honorary chairperson Maude Barlow, meanwhile, said the deal in its current form has "many poison pills".
Before an agreement was reached, the Wall Street Journal reported Trump was already calling it the "USMC", telling Republicans if Canada doesn't agree to the changes, he would drop the "C" from the name.
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. The letters also say Canada and Mexico have to consider whether an automaker is complying with USMCA's auto-content rules - which mandate that vehicle makers source more car parts from North America - when determining how much of that company's production to protect.
Trump defends Hyde-Smith
Trump is holding two rallies Monday to help Hyde-Smith finish the final two years of the term started by Republican Thad Cochran . Hyde-Smith found national headlines in recent weeks after the release of videos showing her making controversial remarks.
Trump since his campaign had called NAFTA the worst trade deal in history, though much of it is carried over in the new version.
"It really is an incredible way to end a presidency", Trump said.
Friday marked an important deadline for the trade pact. It gives USA dairy farmers a bit more access to the protected Canadian market.
With his "America First" approach, general distaste for multinational deals and habit of insulting allies, Trump typically gets a mixed reception at global gatherings. The U.S. continues to push for a quota in exchange for lifting the tariffs on Canada and Mexico, which have applied their own retaliatory levies.
Last year, Rubio said any new trade agreement should increase "oversight and enforcement" of illegal trade practices and that Mexico should have to raise its minimum labor and environmental standards to "limit excessive and unfair production cost advantages" over US farmers.
For Trump - whose G20 diplomacy is overshadowed by legal troubles back home and his abrupt cancellation of a bilateral meeting with Russian President Vladimir Putin - the signing was a victory. "We've taken a lot of barbs and a little abuse and we got there", Trump said. The news ensured any meeting with Putin would have put a spotlight on the U.S. special counsel's investigation into whether the Trump campaign colluded with Moscow during the election. "In the United States, the new trade pact will support high-paying manufacturing jobs and promote greater access for American exports across the range of sectors, including our farming, manufacturing, and service industries".
On Friday, Trump opened the day with a cordial meeting at the Casa Rosada with Argentine President Mauricio Macri, a longtime business acquaintance.