Trump announced his decision before reporters at the White House Rose Garden.
"We're getting out," he said.
Such a move would be a major break from international partners that would isolate the United States in efforts to curb global warming.
EU and Chinese leaders have banded together in an unusual alliance that emphasizes the absence of the United States -- the world's second biggest emitter of carbon dioxide after China -- from the playing field.
Miguel Arias Cañete, EU commissioner on climate action and energy, told CNN in a statement that the two powers "are joining forces to forge ahead on the implementation of the Paris Agreement and accelerate the global transition to clean energy."
"No one should be left behind, but the EU and China have decided to move forward. Our successful cooperation on issues like emissions trading and clean technologies are bearing fruit. Now is the time to further strengthen these ties to keep the wheels turning for ambitious global climate action."
The two spell out their continued commitment to the deal in a draft joint statement, obtained by CNN, which is slated to be published Friday at an EU-China summit.
"The EU and China consider climate action and the clean energy transition an imperative more important than ever," the draft statement says, and "commit to significantly intensify their political, technical, economic and scientific cooperation on climate change and clean energy."
The powers also "underline that tackling climate change and reforming our energy systems are significant drivers of job creation, investment opportunities and economic growth," according to the draft statement, which also emphasizes the importance of international collaboration in curbing global warming.
Speaking alongside German Chancellor Angela Merkel in Berlin on Thursday, Chinese Premier Li Keqiang said his country had "stayed true to its commitment" in fighting climate change over the past few years, including "promoting the signing of the Paris Agreement."
Li said: "Fighting climate change is a global consensus, not invented by China," an apparent reference to a tweet Trump once made
on the subject.
Merkel said she was pleased China was sticking to the Paris climate accord, adding that "the cooperation of the European Union with China in this area will play a crucial role especially in regards to new technologies."
An appeal to Trump via Twitter
European Council President Donald Tusk made a direct appeal to Trump early Thursday not to pull out of the Paris accord, tweeting "@realDonaldTrump please don't change the (political) climate for the worse."
Meanwhile, European Commission President Jean-Claude Juncker said China was prepared to fill the leadership vacuum left by the United States.
Speaking Thursday at a European forum in Berlin, Juncker referred to last week's G7 meeting in Taormina, Sicily, saying: "We explained to Mr. Trump in Taormina that it would not be good for the world or the United States if America was to literally step off the world's stage. Because the vacuum will be filled, and the Chinese are in prime position to take on a leadership role."
In a speech the day before, Juncker said world leaders had tried to warn Trump that he could not exit the Paris Agreement -- ratified by the United States last year -- overnight. "It seems this attempt did not succeed, but the law is the law. And everyone has to stick to it," he said.
He added: "We are not only talking about the future of European people, we are first and foremost talking about the future of people elsewhere. Eighty-three countries are in danger of disappearing from the face of the Earth if we do not begin combating climate change in a resolute way."
Kremlin spokesman Dmitry Peskov told CNN that Russia, another major carbon emitter, also fully supported the Paris accord.
"You know that President (Vladimir) Putin signed this convention, Russia pays a lot of attention (to that)," Peskov said. "Of course the effectiveness of implementing this convention without the key participants, perhaps, will be hindered. But there is no alternative as of now."
UN Secretary-General Antonio Guterres told reporters that Trump's announcement was "obviously a very important decision" since the United States is the world's biggest economy, but that it was vital also that other nations stay the course.
"The Paris Agreement is essential for our collective future," he said, urging civil society and businesses also to play a role.
'A sad day'
International reaction was swift following Trump's announcement, with many leaders accusing the President of turning his back on the world.
"A sad day for the global community, as the US turns its back on the fight against climate change," tweeted EU Commissioner for Climate Action & Energy Miguel Arias Canete. "EU deeply regrets this unilateral decision.'"
Margot Wallstrom, Sweden's minister of foreign affairs, also lamented the decision. "The US decision to leave the #ParisAgreement is a decision to leave humanity's last chance of securing our childrens future on this planet," she wrote on Twitter.
Vicente Fox Quesada, former president of Mexico, was particularly critical of the US President.
"Withdrawal from #ParisAgreement, @realDonaldTrump condemns this generation and those to come. He's declaring war on the planet itself."
In Paris, City Hall was illuminated with green lights to reaffirm the city's support for the climate agreement.
A statement from Anne Hidalgo, mayor of Paris, called Trump's withdrawal "a mistake with fatal consequences."
Trump's decision also received a cold reception in the United States, where 61 mayors signed a statement vowing to "adopt, honor, and uphold the commitments to the goals enshrined in the Paris agreement."
"We will continue to lead. We are increasing investments in renewable energy and energy efficiency. We will buy and create more demand for electric cars and trucks. We will increase our efforts to cut greenhouse gas emissions, create a clean energy economy, and stand for environmental justice," the statement said.
Among the signers were New York City Mayor Bill de Blasio and Mayor Muriel Bowser of Washington.
Elon Musk, CEO of Tesla and SpaceX, followed through on his threat
to leave the President's economic council if the US withdrew from the Paris accord.
"Am departing presidential councils," Musk tweeted. "Climate change is real. Leaving Paris is not good for America or the world."
The Paris climate agreement was established during a 2015 conference in the French capital. Every nation signed on minus two: war-torn Syria and Nicaragua, which insists the deal isn't tough enough.
In signing onto the accord, countries pledged to reduce greenhouse gas emissions, but were given wide leeway in how much they planned to reduce them by.