The deal will still need to be approved by the legislatures of each of the three countries.
The US, Mexico and Canada today signed a new deal governing the more than one trillion dollars (£780bn) worth of trade between the three countries. A senior White House official said Trump and bin Salman exchanged pleasantries during a subsequent leaders' session.
Trump expressed confidence Friday that the pact would sail through Congress.
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.
The deal - 32 chapters, 11 annexes and 12 side letters - sets new rules for the auto sector, including a higher threshold for North American content and rules requiring that 40 per cent of vehicle parts be made by workers paid at least $16 an hour.
But it actually remains far from certain that the agreement would pass the two chambers, particularly in its current form.
Democratic House Minority Leader Nancy Pelosi - who is seeking to become House speaker in the new year - quipped, "The trade agreement formerly known as Prince - no, I mean, formerly known as NAFTA, is a work in progress". The liberal firebrand denounced the agreement as written, saying it wouldn't prevent outsourcing or raise wages. Some Republicans have come out strongly against a labor provision that aims to protect workers from sex-based discrimination. "The new NAFTA preserves tariff-free access in the North American trading bloc and secures essential cross-border supply chains that make North America more globally competitive" said the Honorable Chrystia Freeland, P.C., M.P., Minister of Foreign Affairs.
While many in the USA manufacturing and agricultural industries applauded the deal, they warned that the administration's failure to remove the tariffs enacted during the trade dispute will hamper any benefits they would see from the deal. But he acknowledged that the administration could emphasize certain things in the implementing legislation and include provisions to address lawmakers' concerns to win their support.
US Fed says another rate hike "likely to be warranted fairly soon"
After the financial crisis erupted in 2008, the Fed kept rates at historically low levels to revive the ailing economy. As a result, "almost all" Fed members said a rate hike "was likely to be warranted soon".
Within hours of the signing, Senate Democratic Leader Chuck Schumer said the deal must have stronger labor and environmental protections in order to get majority support in Congress and "must prove to be a net benefit to middle-class families and working people". Democrats and their allies in the labour movement are already demanding changes to the agreement.
"I look forward to working with members of Congress and the USMCA partners - and I have to say it's been so well-reviewed, I don't expect to have very much of a problem - to ensure the complete implementation of our agreement", he said.
At the USMCA signing ceremony, Trudeau attempted to press the US president on steel and aluminum tariffs. The expectation had initially been for those details to be worked out before the negotiations concluded, and then before the pact was signed.
The signing came at the front end of two days of tough diplomacy for Mr Trump.
Trump has continued to accept the crown prince's claims of innocence, just as he has accepted Putin's insistence that he did not interfere in the 2016 election - despite, in each case, USA intelligence agencies' conclusions to the contrary. "It's something we're turning our attention to", he said. "We're not going to take a pause". "We have challenged and are continuing our legal challenges".
As the G-20 summit began, much attention focused on whether Trump would engage with either Russian President Vladimir Putin, a day after abruptly canceling their scheduled meeting here, or with Saudi Arabian Crown Prince Mohammed bin Salman, whose alleged complicity in the murder of USA -based Saudi journalist Jamal Khashoggi has roiled relations between his country and the United States.
The biggest changes target the auto industry. Trump's tariffs on steel and aluminum also remain a sore point for Canadians, Sosnow said. The Global Automakers, meanwhile, called it "unfathomable" that the metals tariffs had "not been resolved in the context of these negotiations".
Trudeau has been referring to the deal as "the new NAFTA", despite Trump's heavy criticism of NAFTA, having sought to replace it since he took office in 2017.