Robert Lighthizer, the United States trade representative, sat with members of his staff in the Senate gallery looking on as senators cast their votes. At least one senator, Republican Rob Portman of Ohio and a former trade representative, walked upstairs to chat with him during the vote.
In 1993, NAFTA passed the Senate on a 61 to 38 vote, and the deal has since been criticized by lawmakers across Capitol Hill for enabling the flow of American jobs to Mexico. A substantial part of the new agreement is dedicated to updating that original text, adding revised guidelines for food safety, e-commerce and online data flows, as well as anti-corruption provisions.
But there are significant changes in the deal negotiated by Mr. Trump’s trade staff and Democrats, including higher thresholds for how much of a car must be made in North America in order to avoid tariffs. It rolls back a special system of arbitration for corporations that has drawn bipartisan condemnation, and also includes additional provisions designed to help identify and prevent labor violations, particularly in Mexico.
Support from a number of prominent labor voices, including the A.F.L.-C.I.O.’s first endorsement of a trade agreement in 18 years, helped firm up the support of Democrats like Mr. Brown, Mr. Wyden and Senator Elizabeth Warren of Massachusetts, a contender for the Democratic presidential nomination.
The only Republican to vote against the deal was Senator Patrick J. Toomey of Pennsylvania, who on Wednesday criticized it as “a badly flawed agreement, an agreement that restricts trade rather than expanding trade.”
Democrats who opposed the plan did so mainly out of concern about the deal’s lack of provisions to combat climate change. Those voting against the pact included Senators Kamala Harris of California, Bernie Sanders of Vermont, another presidential contender, and Chuck Schumer of New York, the minority leader. Senators Cory Booker of New Jersey, Kirsten Gillibrand of New York, Brian Schatz of Hawaii, Edward J. Markey of Massachusetts, Sheldon Whitehouse of Rhode Island and Jack Reed of Rhode Island rounded out the nine Democrats who voted against the deal.
“When it comes to climate change, the agreement still contains many of the same flaws of the original Nafta, which I voted against,” Mr. Schumer said in a statement on Thursday.