President Obama rejected TransCanada’s permit to build the Keystone XL pipeline on Friday, ending a years-long fight that helped reinvigorate the environmental movement and slow the momentum of fossil fuel ambitions in North America.

The State Department, which has been reviewing TransCanada’s permit application, decided the pipeline “would not serve the national interest of the United States,” Obama said during a press conference at the White House, adding “I agree with that decision.”

Obama said the pipeline, which would have carried approximately 800,000 barrels of oil from the Alberta tar sands in Canada to refineries in Texas, was ultimately rejected because it wouldn’t have made “a meaningful, long-term contribution to the U.S. economy.” It would have failed to create a significant number of jobs, lower U.S. gas prices and increase the country’s energy security, he said.

He also cited the project’s contribution to climate change for his rejection.

The project would be neither a “silver bullet for the economy” nor “an expressway to climate disaster,” Obama said, flanked by Vice President Joe Biden and Secretary of State John Kerry. But “if we’re going to prevent large parts of this earth from becoming not just inhospitable, but uninhabitable…we must act not later, not someday, but right here, right now.”

Kerry echoed Obama’s sentiments in a press statement, saying, “The critical factor in my determination was this: moving forward with this project would significantly undermine our ability to continue leading the world in combatting climate change.”

The decision comes a day after the New York State Attorney General announced a sweeping investigation of ExxonMobil for allegedly deceiving the public and shareholders about climate change, capping off a difficult week for the oil industry.

The Keystone XL rejection was celebrated by environmental leaders and climate experts, who viewed the decision as a consequential moment in the fight against unchecked fossil fuel expansion. It was condemned by fossil fuel interests and Republican leaders, who saw the decision as largely symbolic and driven by politics.

For years, Keystone XL was a major point of contention between Obama and climate activists, who couldn’t understand why the U.S. leader was taking so long to rule on the project. His decision Friday helps cement his climate legacy, green leaders said.

“President Obama is the first world leader to reject a project because of its effect on the climate,” said Bill McKibben, co-founder of the environmental group 350.org that has helped lead the anti-Keystone XL movement in the U.S. and Canada. “That gives him new stature as an environmental leader, and it eloquently confirms the five years and millions of hours of work that people of every kind put into this fight. We’re still awfully sad about Keystone south and are well aware that the next president could undo all this, but this is a day of celebration.”

Green leaders heralded it as a massive victory for grassroots climate activism.

“It took years and a level of activism not seen in at least a generation, but President Obama has heard the calls of the candidate Obama that Americans elected and re-elected to fight climate change,” said Elijah Zarlin, climate campaign director for the activist group CREDO.

Meanwhile, Texas Republican Rep. Lamar Smith, the chairman of the House Science Committee who recently launched investigations into several climate scientists, called the pipeline’s rejection “a loss for Americans.”

“This administration routinely dismisses sound science in favor of its extreme environmental agenda,” Smith said. “In rejecting the Keystone XL pipeline, the president said no to 40,000 new energy jobs. Americans are paying attention. This administration would rather pander to its allies than approve a project that creates thousands of jobs and promotes American energy independence.”

The White House’s decision comes just days after TransCanada asked the State Department to delay its review of the pipeline until the company could finalize a route through Nebraska. The move was seen by many as an attempt to punt the decision until after next year’s election in the hope that a Republican candidate might win the Oval Office.

In its official Record of Decision, the State Department said, “The Secretary of State has determined that issuing a Presidential Permit to Keystone to construct, connect, operate, and maintain at the border of the United States pipeline facilities for the transport of crude oil from Canada to the United States…would not serve in the national interest. Accordingly, the request for a Presidential Permit is denied.”

Jack Gerard, president and CEO of the American Petroleum Institute said the rejection was “politics at its worst.”

“Unfortunately for the majority of Americans who have said they want the jobs and economic benefits Keystone XL represents, the White House has placed political calculations above sound science,” Gerard said. “Seven years of review have determined the project is safe and environmentally sound, yet the administration has turned its back on Canada with this decision, and on U.S. energy security as well.”

Obama said Friday afternoon that he had already spoken with new Canadian Prime Minister Justin Trudeau. In a statement, Trudeau said he was “disappointed by the decision, but respects the right of the United States to make the decision.”

“The Canada-U.S. relationship is much bigger than any one project and I look forward to a fresh start with President Obama to strengthen our remarkable ties in a spirit of friendship and co-operation,” he continued.

Trudeau, whose Liberal Party won control of the government last month in a stunning election upset, has said he will call for stricter environmental review processes for pipelines, but supports the building of the Keystone XL. He is facing increased pressure from environmentalists at home to halt expansion of the Alberta tar sands, including a series of civil disobedience happening this week outside his official residence in Ottawa.

Democratic politicians, policy experts and environmentalists said the Obama administration’s decision sends a strong signal just weeks before climate treaty negotiations in Paris, and could help boost momentum for an international agreement.

“Today’s rejection of the Keystone XL pipeline is a victory for our environment, for our communities, and for our country,” said Democratic Senator Brian Schatz of Hawaii. “It gives us more momentum and credibility going into the climate talks.”

Jennifer Morgan, the global director of the Climate Program at the World Resources Institute, said in a statement, “the rejection of the Keystone pipeline is a signal that should reverberate to all parties involved in the Paris climate talks.”