The front runner for the 2016 general and Democratic elections said on Tuesday that she is against the Keystone XL pipeline.
"I think it is imperative that we look at the Keystone pipeline as what I believe it is — a distraction from important work we have to do on climate change," she said during a community forum in Des Moines, Iowa.
"And unfortunately from my perspective, one that interferes with our ability to move forward with all the other issues — Therefore I oppose it."
Ms Clinton had previously not taken a position on the controversial 1,179-mile project, which is vehemently opposed by progressives in the states.
NBC News reports that Vermont Senator Bernie Sanders and former Maryland Governor Martin O'Malley both issued statements regarding Ms Clinton's announcement.
Senator Sanders wrote: "As a senator who has vigorously opposed the Keystone pipeline from the beginning, I am glad that Secretary Clinton finally has made a decision and I welcome her opposition to the pipeline. Clearly it would be absurd to encourage the extraction and transportation of some of the dirtiest fossil fuel on the planet."
Meanwhile, Mr O'Malley was more critical of her stance.
"On issue after issue — marriage equality, drivers licenses for undocumented immigrants, children fleeing violence in Central America, the Syrian refugee crisis, and now the Keystone Pipeline, Secretary Clinton has followed — not forged — public opinion," he said.
"Leadership is about stating where you stand on critical issues, regardless of how they poll or focus group."
Republican National Committee Chairman Reince Priebus would later release the following statement on Ms Clinton's announcement:
“Hillary Clinton insisted her work on Keystone at the State Department prevented her from taking a position on the pipeline, and now we know she was being blatantly dishonest," he said.
"Clearly, Hillary Clinton’s rapid decline in the polls and the prospect of the Vice President entering the race caused her to change course. But instead of backing a job-creating project the American public overwhelmingly supports, Hillary Clinton has sided with extreme special interests, reinforcing how out of touch she is and that she’ll say or do anything to get elected.”
